| Author | Message | ||
     Mnscrounger |
This is a mutant Blast I admit I knew wouldn't run right, but I thought it would be an easy re-jet and I'm on my way. Though I also admit carb tuning is not my strong suit. As purchased, it had a gutted baffleless straight through Sportster "muffler". The bike starts with what sounds like good compression, and idles nice. While in warm up I can even ride it a bit. The problems begin when the bike is warm and the auto enrichener opens up. I knew that exhaust was a problem so I didn't worry much, and I got a good buy on it. First thing I did was put a more reasonable Supertrapp 3" universal can on with 7 discs to try to give it some back pressure. It toned down the bike to a modest level, and I know others here are running a similar muffler, but the problem remained. I tried more and less discs to play with the flow but it seemed to make no difference. Next step was to rejet the carb to the community recommended 45 pilot, 175 main and I confirmed the passages are clear and clean while I was in there. I start the bike up and idling with the air cleaner off, I can see the enrichener raise up and down with the revs. I don't know what normal AE operation would look like, so describing, it never really opens up all the way, it just sort of jitters up and down with the engine rpms but appears to be working. I tried blocking it open once warm and that only made the bike die and not restart until I removed the block. I checked the fuel tank vent and lines to make sure there was no plugging. The problem persists. When warm it falls flat off_idle. I'm looking for suggestions on where I might look next. Thank you for reading. | ||
| Gearheaderiko |
Check the intake boot. It MUST be a stock boot-makeshift boots fail. Take the boot off to inspect it. You’re not looking at the AE going up and down. Check to see if the vacuum port on the carb is plugged and the cap is not cracked. | ||
| Missionbolts |
I don't think it's possible to see the portion of the auto enrichener that moves, while the engine is running. Not without making some extra effort! It's hidden behind the left front of the carb body, where you can't see it if you're looking straight into the opening of the carb with the airbox lid removed And it certainly should not behave as you describe, but the throttle slide is easily visible & does act like that... The auto enrichener does something more than just add extra fuel, it raises the idle speed. So the AE actually has two circuits controlled by the one piston valve. It adds more vacuum signal to the top of the diaphragm, which then acts to raise the main throttle slide higher than when the AE is fully warmed up. If that vacuum port isn't sealing shut properly, the engine will die whenever you open the throttle because the secondary fuel circuit will not be flowing even though the throttle is opened up for more airflow. I think it's a bit of a goofy design, but mine is still working fine, so I'm leaving it alone. This extra feature of the AE is easy to miss, and can really add to the confusion when everyone wants to blame the intake boot. It makes the carb act like there's a major vacuum leak! And often this is why perfectly good intake boots get thrown across garages... | ||
| Mnscrounger |
Thanks to both of you for your input. I've learned something today. So that throttle slide jittering is not actually the AE, its just a vacuum operated "flap", similar to the top butterfly on the secondaries of a GM Quadrajet? that makes sense as that carb bore seems big for a 500 cc motor. Side note: I used to pester on overcarbed big blocks with my AMX using that little vacuum trick. The other guys would mash the throttle without getting the revs up first. Vacuum goes to zero, fuel flow quits, until the motor coughs enough to get vacuum again. By the time their car is back up to @$$ kicking power, the 1/2 block "race" is over. Revving a Rambler only made them laugh, until the tires hooked and the car went straight up on the tourque links. I can't say when I'll get back to it but you've given me a few more things to check when I do. Sounds like since both are unknowns as to condition, an intake boot and a cap are two purchases worth the money for process elimination. It's a cute bike that promises to be fun, and I'm anxious to get out on it. Thank you | ||
| Missionbolts |
"flap" isn't really the best description for what is a typical CV carb's throttle slide As you may have seen, on the Blast that throttle slide moves up & down in a linear fashion. The throttle cables coming back down off of the handlebar do not directly move that slide, but are instead connected to a butterfly valve in the front half of the carb That butterfly valve will look & operate like that Quadrajets main throttle shafts. You do have the approximate right idea. When the butterfly valve is opened, that allows an increase in vacuum back upstream where the main throttle slide is at. There's a vacuum passage that runs up to the top of the carb where the cap is at, and under that cap is a vacuum diaphragm. This diaphragm is what actually opens up the main slide The reason the slide is bouncing has to do with the nature of the airflow through the intake. The engine does not pull air through the carb while the intake valve is closed, so at idle the airflow is pausing for really long amounts of time. Long enough that the slide has time to fall back down from a lack of vacuum signal So for that Quadrajet to be just like this CV carb on the Blast, it would need to have the primaries blocked-off and only use the secondaries You are also correct on how big that Blast carb is vs the engine size. The intake port is also that big, and it really is just a bit 'overcarbed' After the engine warms up, with the airbox lid off and idling, you can see gasoline misting outwards just in front of the carb's inlet because the airflow is reversing and picking up fuel on it's way backwards through the carb The head design on the Blast motor is taken from the bigger V-Twin XB which had 669cc per jug. The Blast project required an absolute minimum of R&D, so many things like the port size & shape were literally a cut & paste job There's a well-known bandaid fix for the oversized intake port that basically is adding a splitter plate that is almost touching the main throttle slide. At low throttle positions, this plate keeps the airflow coming off the bottom of the slide in a smaller cross-section of the intake boot & port. That results in the airflow moving faster. Which prevents reversion effects at idle & the off-idle performance becomes much better And, the reversion issue is also part of why the throttle slide has so much 'bounce' at idle I would just look at the intake boot and cap for any sign of cracks. The boot should be flattened a little bit in order to flex the outer skin apart. That will spread open any cracks that are hard to see As for the cap, I would just rig up a test plate to use with the hand pump on my brake bleeder kit. A plexiglass plate with a hole drilled in it and a vacuum port set over the hole with JB Weld or epoxy. The cap has an o-ring seal, so it should seal itself to the plate while drawing vacuum. If the test rig holds a vacuum, I would dunk that in a bucket of water to see if any cracks are letting water get inside. I could test the intake boot the same way, but it's easier to just look at it | ||
| Mnscrounger |
Missionbolts: That is absolutely one of the best function explanations I have ever read! You described exactly what I am seeing. I hadn't really understood the reason for the "splitter" mentioned elsewhere in the Thumper section and I really like that idea, I might have to fab one up. But I understand that is no substitute for proper troubleshooting and tuning. As I said In any case I will be picking up a boot, (for 16 bucks and change at SPHD, its a cheap factor for process elimination), and while I'm there I'll see if they have a replacement cap too. Thank you again | ||
| Gearheaderiko |
Just to clarify: the Blast head has very little in common with an XB head. The Blast head is mostly a pre-2000 Sportster head-which one I couldn’t tell you, mostly because there are much better performers available. The “cap” I mentioned is just a vacuum port that was only used on California blasts and it just needs a good $1 plug. Some Blast carbs don’t even have that port drilled out. No test is necessary. Thanks for taking the time to write all that up. It is very much appreciated. | ||
| Missionbolts |
I've been tempted to install a five layer splitter stack, but each extra plate will add more drag to the airflow I would do that so the throttle slide is more closely matched to an appropriately-sized passage, at all throttle positions. But the Blast just isn't impressing me as a performance project bike like an XB would be My impression of the Blast is it's really just better at commuting & pushing for 50 plus miles per gallon. So I'm only going to do a few minor upgrades to make it better as-is. Fork oil got changed out to a bit thicker. Going to fab up some sort of wind break for the hand grips and a bullet style windshield | ||
| Mnscrounger |
Agreed its not a good candidate for a performer. Its a "mutant now with an XB swing and XB12R front end, clip on bars and all,(and it looks really cute, kinda like a seven year old with a cape). Once I get it running as is, and confirm it's worth the time, I will put the Blast forks back on, wider dirt tracker bars, and replace the rear swing with a Uly version. That should give me enough clearance for some 19"f 18"r KZ wheels and a 60T sprocket I've collected. It won't be fast, but it should be fun for banging around on logging roads and trails. | ||
| Missionbolts |
Guess I don't know the engine's history well enough! I only looked into how it relates to an XB and stopped there. Sportster still has a much larger engine, and I can see the reversion effect on my Blast. It's the only engine I've ever seen this happen on not counting worn-out chainsaws & weedeaters, but it's also the first american made bike I've ever owned I've been running my Blast on forest roads in bone stock form with the exception of the tires. Both tires are now dual-sport front's, can't recall exactly what at the moment. But I've been able to scrape the foot pegs on pavement without any traction issues, so I'm not at all worried about ditching the sport tires. Plus the rolling resistance of these dual sport tires is much lower. Mainly from being very skinny, but also because the contact patch is more free to flex across the road surface, being composed of many small lugs instead of one single lug. The suspension bottoms out too much and the muffler has a 2" dent in the bottom from hitting a rock while I was going up an abandoned high ridge road. That impact also resulted in breaking the front mounting tab on the seat. Both rear turn signals broke off after snagging on scotchbroom and have been replaced with custom flush mount lights. I broke the drive belt while riding in deep snow. The snow packed up in between the belt and drive pulley. So I've been thinking about converting to chain, mainly after finding out that there's reasonably-priced timing belts in the industry that would have fit if Buell had just made the rear swingarm an inch longer. That would've saved on the production cost I would recommend beefing-up the Blast forks with stronger springs and a bit thicker oil. The travel is limited for off-road, and too weak. I've slammed the forks all the way to the bottom without even trying all that hard | ||
| Mnscrounger |
I replaced the boot, and checked the vacuum port cap for leaks, (none found). I started the bike back up and the problem is still there so I took my MAP gas torch and turned on the oxygen. I found a little bit of a leak around the intake at the head. I have a feeling it's not just a plain old 1/8" round O ring that's supposed to be there, but that's what I found. I would expect that to be a square ring to seal the intake. I'll pick up another seal this week and try again. (Message edited by mnscrounger on February 03, 2020) | ||
| Gearheaderiko |
If it’s the intake to head mount, it is just an o ring. But if someone tightened it too much that can warp the manifold. | ||
| Mnscrounger |
based on the ring gland .072 D X .132 W, I would have expected either a square o ring, or one larger that the .093" ( 2mm?) cross section diameter one I found in there. it just looked really loose in the gland groove. I will replace it with a 1/8" diameter version that looks more appropriate for the function.   | ||
| Missionbolts |
That small o-ring does look a bit suspicious. But what really matter is how far outside of the groove it's sitting & how well it matches up with the sealing surface on the head If you really want an x-ring, and in a more durable material, while not paying more than you should, take a look at this outfit: https://theoringstore.com/ They have 1/8" cross-section x-rings in nitrile, from 5/8"~12" OD. One of those might just fit For example, the 2" OD is available in single piece orders( up to 10,000+) for only 43-cents plus a stamp. And all the o-rings I've bought from them were delivered very promptly with candy slipped in for the fun of it | ||
| Mnscrounger |
According to the Parker O-ring design guide, a static face seal with 20-30% compression should be good. The measured groove dimensions are deeper, but close to the right depth, but are way too wide for a 3/32 ring. The depth is less than recommended for a 1/8"ring, but about the right diameters. It could be Buell was just under machining the groove and expecting some extra squeeze to compensate for the rubber extruding all the way into the gland groove corner radii at higher temps. | ||
| Mnscrounger |
According to the Parker O-ring design guide, a static face seal with 20-30% compression should be good. The measured groove dimensions are deeper, but close to the right depth, but are way too wide for a 3/32 ring. The depth is less than recommended for a 1/8"ring, but about the right diameters. It could be Buell was just under machining the groove and expecting some extra squeeze to compensate for the rubber extruding all the way into the gland groove corner radii at higher temps. | ||
| Missionbolts |
I think that compression guide might depend on shore hardness rating. 20% for 90A, 30% for 50A Having excess groove width after compression could allow the intake pulse to shift the o-ring around that it might leak If I were to make any changes for that o-ring, I'd consider a higher temp rated material than Buna-N. Viton would be good, maybe silicone too. I would consider long-term resiliency plus rating for above 300°F Just had to deal with my Blast not wanting to turn over. Turns out the harness connectors behind the headlight do not have any form of weatherproofing seals. And no grease either. Basically, the killswitch wasn't able to do it's part and the entire system was dead. I got the engine to turn over using a jumper wire right at the starter, only to find that there wasn't any spark either Thinking about chopping the connectors out and soldering the harness together And my exhaust is broken off at the head again, but I'm kinda digging the extra power. Just wish it wouldn't sound like a steel box of rocks every time I let off the throttle | ||
| Mnscrounger |
Well replacing the intake seal didn't solve it either. I know the common wisdom is to go no deeper in the carb than the jets, but I have no guarantees any of the POs followed this wisdom. I could put the stock muffler back on to see if that's the cause, but I've seen enough "other" exhausts that I doubt that as the problem, as the bike doesn't just run poorly it absolutely falls flat. Does anybody have a confirmed good carb sitting on a bench that I can borrow for diagnostic purposes? | ||
| Missionbolts |
I've never subscribed to the common lore. I would think that never checking the entire carb can be the reason why it's not working right. The auto choke itself can fail without anything obvious - if you remove it to look it over. And it does have the ability to cause the problem you are dealing with. If you were in the west puget sound area, I'd pull my carb and let you try that out for testing | ||
| Mnscrounger |
yeah I just spent a good deal of my day off looking at Leland Fried's youtube postings about the Blast CV 40. I have a bit more confidence to go a bit deeper next time im out in the garage. | ||
| Gearheaderiko |
A lot of people “give their carb a good cleaning” because they were told that by someone else who had no idea what the problem is or hasn’t much of an idea how carbs (or the CV carb) works. This creates most problems of the people that show up looking for help. Generally things don’t go wildly wrong on their own and a torn boot is very commonly the problem. If it runs okay cold, then you likely have a warm up lean issue. Unplug the TPS and that should temporarily solve your problem enough to find out how the bike runs. Instead of pulling things apart, look for an intake leak with some Brakleen or carb and choke cleaner (or just about anything that will burn and not do damage). A torn or misassembled diaphragm is a common malady. A small “barrel shaped piece” that the tip of the needle slides through often gets put back in wrong. The needle can also be put back in wrong, especially if someone has tried to shim it. If you haven’t tried unplugging the TPS, please try it. Also, if you use the wrong intake O-ring and/or over torque it, that can lead to an intake leak. (Message edited by Gearheaderiko on February 23, 2020) | ||
| Mnscrounger |
Thanks, for your help and encouragement guys. I finally got around to looking deeper and trying your suggestion of disconnecting the TPS/AE connector. While looking into it I did manage to free up the AE adjustment, and check the resistance to confirm no shorts or opens. (4 ohm across the AE). also I adjusted it to middle of the port when cold, and checked the diaphram for tears. It seems to be fine everywhere I look, but off idle it still dies and the exhaust looks really rich coming out the pipe. The plug does not look fouled. and there seems to be good compression. I'm beginning to wonder if I ought to start looking elsewhere. ECM or CPS possibly? | ||
| Gearheaderiko |
There is no ECM and I don’t know what a CPS is! The ignition is very basic. The ignition module under the timing cover takes place of the traditional points and spark advance. Then there’s the coil, that’s it. Did disconnecting (unplugging the wiring harness at the AE and TPS) and running with it unplugged change anything? | ||
| Missionbolts |
Mnscrounger - I would think by 'ECM' you mean the ignition module. The TPS does hint at there being some sort of computer in the works, so you're not really that far off. (there really is a micro-processor inside the ignition module, the ignition advance is done with software) And 'CPS' (Crank Position Sensor) would be the ignition timing pickup. The timing pickup is built into the ignition module and not easy to test by itself But, the engine does start & idle. So that means the timing pickup is working fine. And the timing might not be too far out of whack. You might want to check that. The ignition module can be loosened & moved in order to adjust the timing On the outermost right-hand sidecase is a small round cover that has to be pried off to access the ignition module, unless your bike is like mine and the cover flew off & hit someones windshield like all my exhaust bolts seem to keep doing The timing mark is hidden behind a allen-keyed plug on the right-hand side, at the bottom of the cylinder. Kinda looks like an oil drain plug. With the plug removed, you're looking right at the outer edge of the crankshaft where the timing marks are clearly stamped. With engine idling, shine a timing light into that hole and move the ignition module. You just line the mark up with the center of the hole & lock the module down Something I've had happen before is a cracked ignition coil that would run ok at idle but completely die under load. The secondary voltage would stay just low enough at idle that it couldn't jump the gap where the coil was cracked, but under a load the voltage would go high enough to short out the sparkplug I know this might sound a bit weird, but what I would do is mount a timing light on the handlebars where I can see if it stops flashing when the engine dies. That will tell you if the issue has anything at all to do with the ignition cutting out on you due to a bad module, coil or something | ||
| Mnscrounger |
"Ignition module" instead of ECM, "timing pickup", instead of CPS. Got it. ( Can you tell my other bike is an injected tuber?) I just happen to have a timing light laying around. I will give that handlebar mounted test a shot next time I'm in the garage. Thanks | ||
| Missionbolts |
No matter how well the bike handles, the engine is really just a glorified lawnmower engine when compared to anything else out there. Really shouldn't be pushing it past 4000rpm's, every nut & bolt needs to be locktighted or safety-wired because the engine shakes so much, clutch cable, primary chain adjuster and shift shaft are all running below the tranny oil level, so if those stop leaking - it's time to pour more in! Shifter shaft oil seal needs to be replaced everytime you remove the left-hand sidecase. I really wish Eric Buell had been working for Cannondale instead! | ||
| Gearheaderiko |
Well most of that is BS! The lower the rpm, the more it shakes and you can run it up to 7500rpm all day long without issue, if you have the ignition and valve springs. | ||
| Missionbolts |
Sorry Gearheaderiko, but I kinda already agree with what you're saying there | ||
| Mnscrounger |
"the engine is really just a glorified lawnmower engine" I think that's why it's so frustrating to troubleshoot, and FAIL. I keep telling myself "Its so ''''ing simple, what am I missing?!" | ||
| Missionbolts |
If the spark stops, that would make it fail Just for luck, I'd change the sparkplug. I've had bad plugs before, usually Champion or Autolite. Which is why I always buy NGK for anything that burns gasoline Something I've done a few times before is to look an ignition system over while running on the kickstand. I do this at night with all the lights in the shop turned off. If the coil or plug wire is shorting out, I'll see little blue/white sparks And there's still a chance that maybe your carb isn't setup right. And also a chance that the ignition is the 1st issue & the carb will still need fine tuning A long shot could involve checking that the engines cam is timed correctly |
