Erratic idle & Backfire

[Prestone]

I had rust in the fuel tank which clogged the fuel filter, etc, etc. After sealing the tank, I removed the carbs & cleaned all the rust from the float bowls. After re-installing them, it runs terrible. Idle goes from 3000 RPM down to 1500 & back up. When it idles down, it pops through the RH, rear carb & backfires big time out the exhaust. I have cleaned idle jets mutiple times & checked float levels which look good. I was thinking big time vacuum leak, but when I spray WD 40 around the intake manifolds, nothing changes. I guess I could be missing the actual leak when I spray it. I put my Carbtune on it & at about 1,500 (when it will stay there), the two RH cylinders are registering very low vacuum, barely on the scale. It has to be a leak, correct? With it being both cylinders, would almost have to be the V-boost interconnect? I just want to fix it as the riding weather in South Carolona is getting better by the day. Thanks for the help

 

[dannymax]

I had rust in the fuel tank which clogged the fuel filter, etc, etc. After sealing the tank, I removed the carbs & cleaned all the rust from the float bowls. After re-installing them, it runs terrible. Idle goes from 3000 RPM down to 1500 & back up. When it idles down, it pops through the RH, rear carb & backfires big time out the exhaust. I have cleaned idle jets mutiple times & checked float levels which look good. I was thinking big time vacuum leak, but when I spray WD 40 around the intake manifolds, nothing changes. I guess I could be missing the actual leak when I spray it. I put my Carbtune on it & at about 1,500 (when it will stay there), the two RH cylinders are registering very low vacuum, barely on the scale. It has to be a leak, correct? With it being both cylinders, would almost have to be the V-boost interconnect? I just want to fix it as the riding weather in South Carolona is getting better by the day. Thanks for the help

Think I'd start with the shotgun and peashooter Prestone.

 

[Prestone]

Thanks for the quick reply Dannymax. Been there done that with the shotgun & peashooter. I did it a second time to be sure. Pilot jets are all clear.

 

[KJShover]

Have you checked for cracks and whatnot around the boots and airbox? Also it's pretty easy to put the carbs back on and have them not be fully seated. I've done that a few times.

 

[Prestone]

I think tomorrow I'll pull the carbs back off & take a good look. Spraying WD 40 didn't change the way it ran, but I may be missing the leak if it's in a tough spot. I've had them off & on enough, maybe I've disturbed something or cracked a hose. The more I think about it almost has to be a big vac leak......

 

[Rhoy Carter]

I would think that there is still a pluggage somewhere in the carbs, how far down r u pulling them when cleaning?

 

[Prestone]

I pulled the float bowls off, removed the float & needle, removed the slides, & cleaned everything out with air & carb cleaner. If there is blockage, which there could be, it's not showing up when I blow through the circuits. I have had my pilot jets plugged up several times before & the shotgun & peashooter always fixed it, but those symptoms were way different. It would just be down a cylinder at idle, but pick it back up once I got up on the throttle. To be honest, it was running much better than this when everything was full of rust. Not sure if I'll have time tonight, but I'm going to take them back off & look everything over really good. If I need to go through the carbs completely, I'll do it, but I'm thinking it's something I did re-installing them. I'm becoming an expert & taking them off & putting them back on, or so I thought. I'll report back on my findings & thanks again for the input.

 

[one2dmax]

I don't see anywhere that you took the jet block out and cleaned the jets inside (under the rubber plugs). The smallest jet of the whole carb system (and the one that controls a lot of the idle) is in there.

Sean

 

[[email protected]]

If its worse now than it was before, I'd say there's either gotta be a mistake somewhere or you have some old boots that are now cracked after all the monkeying around.

Check the stupid stuff like making sure you have the carbs fully seated, the vent tubes are in place and routed properly, the airbox is in place (yes these things matter), that you put the needles together correctly and the little "tit" on the plastic piece is properly situated.

If you tearing the carbs apart to clean when you have the bowls off you really should go and remove the jet block and pull the plugs out of it, remove the jets, and clean all that out. *edit* Sean beat me to this one*

Also, check the rubber hose that goes to the #2 cylinder intake manifold for cracks or kinks.

Drain the fuel from the bowls and inspect it. Make sure you have cured your rust issues.

Are you sure its just not WAY out of synch??? Its possible after being taken on/off multiple times and splitting the rack. Are you sure the linkage from side to side was put back together correctly?

I'm basically just throwing shit out there for ya'. Hopefully somehthing helps!

 

[Prestone]

Great point on the jet block Sean. If I don't see something obvious, I'm going to go back thru the carbs completely. No worries on throwing stuff at me. That's exactly what I was looking for. Thanks a lot guys & I'll keep you up to speed on what I find. I hope to solve this myself, but for future reference, does anybody know a good Vmax wrench in the Charlotte, NC area.

 

[one2dmax]

most of the carb sets I rebuild have the pilot jets plugged which is in the jet block. It will take a very small wire to run through it and clean them out. If you "kreemed" the tank get ready to buy another set of carbs when that crap starts peeling.

Sean

 

[gamorg02]

most of the carb sets I rebuild have the pilot jets plugged which is in the jet block. It will take a very small wire to run through it and clean them out. If you "kreemed" the tank get ready to buy another set of carbs when that crap starts peeling.

Sean

u don't like kreem? what do you use usually?

 

[Prestone]

I used the KBS kit to seal it. I've had good luck on cars with it, but this is my first go around with it on a motorcycle. Guess I'll cross that bridge when & if I get there. Where is the best place to get rebuild kits Sean, do you sell them?

 

[dannymax]

What's a new tank....a couple hundred bucks? I know the way I'd go! unk:

 

[one2dmax]

Either a good used tank or new. A new tank is over $300 now. Used good tanks are hard to come by. Someone recently did their tank with something and can't remember what it was (POR brand maybe)?? Every tank I have ever done or have seen done with Kreem has peeled. When it does you have particles of every size including stuff small enough to get past the filter. BUT, that crap doesn't dissolve so good luck getting it out of the carb bodies.

Watch the filter closely and keep an eye on the tank.

The only kits are keyster and they are big time junk! Got pictures somewhere showing defective brass.

I do have carb parts on hand which all you normally need is the gaskets for the jet block, choke pulloff and a few o-rings and new plugs for the jet block. Not always do the rubber parts need replaced. Most of those parts end up running around $150 for the 4 carbs.

Sean

 

[Prestone]

Either a good used tank or new. A new tank is over $300 now. Used good tanks are hard to come by. Someone recently did their tank with something and can't remember what it was (POR brand maybe)?? Every tank I have ever done or have seen done with Kreem has peeled. When it does you have particles of every size including stuff small enough to get past the filter. BUT, that crap doesn't dissolve so good luck getting it out of the carb bodies.

Watch the filter closely and keep an eye on the tank.

The only kits are keyster and they are big time junk! Got pictures somewhere showing defective brass.

I do have carb parts on hand which all you normally need is the gaskets for the jet block, choke pulloff and a few o-rings and new plugs for the jet block. Not always do the rubber parts need replaced. Most of those parts end up running around $150 for the 4 carbs.

Sean

Sean, I'll do what you think is best. Just tell me the seals you think I'll need & what I need to do to get them. I'm going to go ahead & get things disassembled, inspected, cleaned & ready to re-assemble. Riding season is upon us.....:clapping:

 

[one2dmax]

Shoot me a direct email and we'll get the details sorted out. [email protected]

Sean

 

[Prestone]

Well, it took forever to get the Max put back together. Nothing like work & family to screw up your priorities...LOL

First of all, thanks to all, especially Sean for all the help. I know I was a pest for awhile....

I dissassembled the carbs yet again & removed the jet blocks per Sean's advice. I didn't really find a smoking gun (jets were all clear), but there was still some rust residue in the jet blocks so it needed to be done regardless. I cleaned everything back up & re-checked the float levels.

I really suspected a vac leak from the start so I replaced all of the carb joints & V-boost joints which were rock hard & starting to crack. I also replaced all four intake pipe o-rings. Thanks again to Sean for all the parts.

I could tell right away when I cranked it up that it was 90% better.

It wasn't firing on the Left front cylinder at idle, but after a few rounds of synhcronizing & some test rides, it seems to run like new again. Can't wait for good long trip to ring it out.

Thanks so much to everyone for their input. It is so nice to know that any problem I have with my max, help is just a log in away. unk:

 

[johnnycomelatly]

I have stage 7 after I synch the carbs with v-boost closed, I set the idle at 1000 rpm and then when I opened v-boost back up it idles at 900. Should I just leave it there or put it back up to 1000?