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Message started by azjay on 05/31/06 at 20:51:41

Title: running bad under load
Post by azjay on 05/31/06 at 20:51:41

debby and i went for a short putt tonight, and about 15 miles into our 25 mile ride her bike started acting as though it was starving for fuel. we had just filled both bikes from the same hose(chevron premium), mine runs fine, asumption: its not the gas. rotated the petthingy to PRI, no change, assumption: its not the petthingy. pull the clutch in, rev motor, motor revs fine, assumption: its not the cam chain/valve train. there are no unusual noises coming from inside the engine, the only noticable difference, is more popping in the exhaust, which goes along with the starving. she rode it home, it would go through the gears at lower rpms, but from mid range on up, not,not,not,pop,pop,pop. its a good thing its a thumper and has great torque on the low end. any similar experiences, help or suggestions are welcome, even sympathy is welcome at this point.

Title: Re: running bad under load
Post by Savage_Rob on 06/01/06 at 06:25:13

That does sound like fuel starvation and you definitely have my sympathy. If it were me, I'd pull the petc0ck and check to be sure the screen is clean. I'd also check my inline fuel filter, though I don't know if you've installed one. for dirt/rust/etc. I'd also check the vacuum line to be sure it's not compromised. After that, I'd check the carb for dirt and verify the needle and float operation. If it wasn't for the reported loss of power, I'd suggest looking for exhaust leaks that could cause the backfiring.

Title: Re: running bad under load
Post by MacAttack on 06/01/06 at 07:38:13

I wonder if the slide is sticking. I have a sneaking suspicion that dust gets in from the slide diaphragm's vent (the air needs to be displaced somewhere to let the slide open). I was shocked to see the slide all scratched up with only 1000 miles on the bike. I need to look more closely at the carb - seemed to me part of the slide area was open to the atmosphere, so dust could easily get in. Since I ride on 4 mi. of gravel daily, this is a problem !
Good luck!

Title: Re: running bad under load
Post by Keith_B on 06/01/06 at 09:44:16

The vent hole is in the top cover above the diafram dust shouldn't get to the slide.

Title: Re: running bad under load
Post by Ed_L. on 06/01/06 at 13:20:28

Check the gas cap, there is a vent in it somewhere that can get plugged up and cause a fuel problem. Really does sound like a fuel stavation problem. Check the easy stuff first before tearing into the carb. Luck and keep us informed.

Title: Re: running bad under load
Post by Trippah on 06/01/06 at 14:55:25

Did you do the white spacer "Mod" recently; when I did i did not get the larger spring settled correctly and had similar symptom. Well, thunderstrms approaching bye for now. Good luck and let us know what you find out.

Title: Re: running bad under load
Post by azjay on 06/01/06 at 21:04:04

this condition IS deffinately heat related. i reproduced the problem again today, it was 106* at 4:30pm, and i went on a 25 mile run and as long as i kept moving, it was ok. i stopped at the harley shop for a few minutes(15 miles into the run), and let some heat build while parked. when i left the harley shop it acted up, i pulled over and switched to PRI, it seemed to clear up, so i stopped at the chopper shop, to visit for a few minutes and build some heat again. when i left the chopper shop, it acted up again, BUT, this time it did not clear up, 3 miles home, pop,pop,pop, low rpm under load, pull the clutch in and motor revs fine ???
i pulled the petcock to check the filter, nothing to report there, a tiny bit of dirt, but nothing to be of any concern. as long as i had the petcock in my hand, it seemed like good idea to convert it to a manual type, so i did that. by the time i reassembled the bike for a test ride, the sun was headed over the horizon, and the temp had cooled to something closer to 100*, so the heat wasn't a factor anymore, and the bike ran fine. we will test ride it again tomorrow in the heat of the day. we are supposed to see 110* saturday.

Title: Re: running bad under load
Post by 911radioman on 06/01/06 at 21:11:39

Vapor lock? Don't know how possible it is on these bikes (or any bike for that matter), but it crossed my mind and thought I'd throw it out for consideration.

Title: Re: running bad under load
Post by azjay on 06/01/06 at 21:30:17

that is certainly a consideration. the big city (phoenix/socal) type gasoline has an oxygenator that causes it to burn hotter(smog police) and flash off at lower temps. unfortunately, the suzuki hides its carb behind the head/cylinder, and i think the heat could build up and boil the gas in the carb, heat rises and the gas in the tank is warm/hot too.

Title: Re: running bad under load
Post by Savage_Rob on 06/02/06 at 05:38:57

Well, converting the petc0ck to manual should negate the vacuum line as a possible fault. I guess we'll see what happens next.

Title: Re: running bad under load
Post by azjay on 06/02/06 at 13:36:45

i just got back from a couple test rides, it is currently 110*, the heat index has the "feels like" temp adjusted up at 117*. 1st ride; manual petthingy, bike ran 1.5 miles before acting up :( 2nd ride; added 1oz marvel mystery oil to 1/2 tank of fuel, bike ran 3 miles before acting up :( while riding home i pulled on the choke and it fattened right up, and operated rather normally :-/ it looks like i'm going into the carb again, i think i'll wait a while until the bike cools down (october?) ;D

Title: Re: running bad under load
Post by Dynobob on 06/02/06 at 17:17:02

azjay wrote:

while riding home i pulled on the choke and it fattened right up, and operated rather normally :-/

You're lean. You either have an air leak or something's not right inside your carb (as was suggested by Trippah).

Title: Re: running bad under load
Post by azjay on 06/02/06 at 21:30:01

yep, deffinately lean, the question is; too much air? or, not enough fuel? ???
i just came in from the garage, the carburator is disassembled and i did find a little something, the transient enrichment valve (looks like accelerator pump to me) was a bit sludgy around the sliding surface, perhaps old gas varnished on there, so i cleaned it and the rest of the carb with aerosol carb cleaner and compressed air. i also steel wooled the main slide as it had a slight texture to it, seems to be smoother sliding in the bore now. i am aware, that scientific procedures dictate one change at a time, so that changes can be identified with the associated corrective action, but this carb is such a drag to pull. :( we will test ride again tomorrow.
trippah; were you referring the big spring on top of the slide? i will pay particular attention to that when i reassemble

Title: Re: running bad under load
Post by Trippah on 06/03/06 at 09:22:46

yes. that's the one. I managed to fold it sideways..basic clutz. And I know what you mean, doing 1 thing at a time so you know what was wrong is so scientific, but such a PIA. God luck with the quest.

Title: Re: running bad under load
Post by azjay on 06/03/06 at 18:06:23

FIXED!! ;D currently 112* 8), i just returned from 20+ mile test ride, and there is no hint that the problem ever existed. appearantly, cleaning the transient enrichment valve(TEV) was the cure, i really dont think the slide was the issue. the TEV is accessable while on the bike, carb removal is not required. when i described the problem to my dad, he said the vacuum slide carb sounded like an SU that came on the early triumphs, they also suffered from a similar issue, the text book cure was to remove the TEV(or whatever they called it) wipe it with a clean cloth and reinstall. sounds familiar ??? anyhow, look out highways here we come!! :)