duderadidea Posted September 6, 2012 Share Posted September 6, 2012 Hey all, After having rebuilt carbs, cleaned tank, replaced fuel filter, eliminated fuel pump from system altogether, replaced plugs, tested coils & wires, adjusted valves, I'm about to sell it for parts. This started a few years ago when my stator/rr died on me, and I replaced those along with the battery. After about 1000 miles, it died on the road and I decided the crap I found in the fuel filter and the tank was the cause. After a new filter and a pretty thorough tank cleanse, it died again only 100 or so miles later. Rebuilt the carbs, same thing happened, and since then I've been chasing around this problem and coming up with nothing. I've had the carbs off and taken apart about 5 times now (I was really hoping the 3rd time would be the charm) including having replaced them with a cleaner set off a lower-mileage bike. Here's what's happening at this point: I can usually fire up the bike when it's cold, with the choke on. I rev it up to around 5000 rpm, at which point all cylinders are firing. If I let it drop below 2 grand or so, it'll sink into a weak idle with not all cylinders going. I forget numbers at the moment but I'm pretty sure the left front and left rear are the ones that run reliably. I'll confess that the stages in which I've been working on this have taken place over 3 years or so, and the rest of the time the bike has been sitting in a fairly dry garage. I'm fairly certain that my coils and wires are good, the plugs are new, and the pilot jets are clean. At this point I'm having a hard time wrapping my head around this thing, and all I really want to do is get it running well enough to sell it for reasonable coin! Thanks for reading, any input is appreciated. And it's for sale, so feel free to make an offer. Link to comment Share on other sites More sharing options...
Member Contributer thor294 Posted September 6, 2012 Member Contributer Share Posted September 6, 2012 check the timing chain? make sure everything is lined up Link to comment Share on other sites More sharing options...
squirrelman Posted September 17, 2012 Share Posted September 17, 2012 A timing chain would be very hard to find on that bike. Seems like the problem is within the idle circuit, so i'd suggest using carb cleaner and high-pressure air to blast the idle mixture screw passages. Too much use of eather will damage the piston rings and cylinders. Wouldn't be the first time a rider swore he'd cleaned his carbs but hadn't done the job thoroughly enough. Photo shows one way to be certain the idle jet is clear. Link to comment Share on other sites More sharing options...
Guest Posted September 18, 2012 Share Posted September 18, 2012 Wouldn't be the first time a rider swore he'd cleaned his carbs but hadn't done the job thoroughly enough. +1. The idle mixture screw passageway is very hard to clean well. Sometimes an ultrasonic is the only way. But even without one, it took me three tries to get my own '86 going. Once you put fuel to those carbs, they can't be left sitting for a long time, no matter how clean you left them. You'll have to start over if you leave fuel in there. Link to comment Share on other sites More sharing options...
SEBSPEED Posted September 18, 2012 Share Posted September 18, 2012 Clean the carbs again, maybe with some help this time? Pull the spark plugs too, they could be fouled from the first try. Link to comment Share on other sites More sharing options...
Baileyrock Posted September 18, 2012 Share Posted September 18, 2012 Sounds like a Vtec issue! Still crap in teh carbs like mentioned. BR Link to comment Share on other sites More sharing options...
Member Contributer thor294 Posted September 18, 2012 Member Contributer Share Posted September 18, 2012 I just took his cleaning for granted haha. I know when I cleaned mine (my 86vf500 that I sold) the carbs were so gunked from the bike sitting for 8 years... I soaked the jets in carb cleaner and had to use small wires to clean them out reallllllll good Link to comment Share on other sites More sharing options...
Member Contributer mk2davis Posted September 18, 2012 Member Contributer Share Posted September 18, 2012 I'm a big fan of fresh brass. Maybe it's my own deficiency, but $16 worth of new pilot jets is worth not having to clean them always wondering if I got them TOTALLY clean. EDIT: Rereading the OP, was there any difference with the new set of carbs? It seems unlikely that two different sets of carbs would have exactly the same level of dirt in the same circuits. If you think it's electrical (and I'm just saying this because you mentioned your RR/stator issue), try connecting a timing light to the plug wire(s) you think aren't firing. Link to comment Share on other sites More sharing options...
Beck Posted September 18, 2012 Share Posted September 18, 2012 Does "Seafoam" help to keep these jets clean?? My bike's 17 years old and I never torn down and cleaned out the carbs. I'm hoping that regular doses of Seafoam will keep the gunk at bay,....but at 17 years in there already?....I dunno, it might be just a matter of time, even if I keep the bike driven and refueled regularly...... Beck 95 VFR Link to comment Share on other sites More sharing options...
Member Contributer SamW Posted September 19, 2012 Member Contributer Share Posted September 19, 2012 Does "Seafoam" help to keep these jets clean?? My bike's 17 years old and I never torn down and cleaned out the carbs. I'm hoping that regular doses of Seafoam will keep the gunk at bay,....but at 17 years in there already?....I dunno, it might be just a matter of time, even if I keep the bike driven and refueled regularly...... Beck 95 VFR My experience is yes, and it will clean your carbs to a certain extent. After a few months of non use on my '86, I put fresh gas and seafoam in my tank and few miles down the road I had a bad miss, turned out to be a little carbon/trash got between the float valve and the hole and flooded one cylinder. I drained the carbs, tapped on them, fired it up and no more miss. Could it have been something else that loosened the carbon/trash? Sure, but seems pretty connected. Will it fix an already clogged jet, doubt it, but that is why you buy Yamaha carb soak. Link to comment Share on other sites More sharing options...
FTM Posted September 27, 2012 Share Posted September 27, 2012 Vacuum in the tank maybe ? Could be fuel starvation caused by a blocked breather hole in the petrol tank. Try running the bike with the fuel cap open slightly (not out on the road obviously). Link to comment Share on other sites More sharing options...
Guest Posted October 7, 2012 Share Posted October 7, 2012 I remember a case of a VF400 having troubles working below 4K and the culprit was one of the CDi boxes. Link to comment Share on other sites More sharing options...
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