Carbs are screwed

[Meister]

Hi everyone, new member here. I've spent the last few hours perusing the carb section looking for the answer to my questions, but to no avail. I'm pretty good with carbs after many years of jetting and tuning race bikes from the mid 90's on. This bike has me stumped! I've bought a 94 Vmax that didn't run for 7 years.

The gas was gummed in the carbs so I pulled them and cleaned them out one by one. The only thing I didn't disassemble was the small assembly in the back of the bowl where the needle rides. After ultrasonic cleaning them and reassembly I noticed some gum reappeared on the needles. I disassembled the diaphragm and needle assembly and cleaned the areas where gum showed up. Float levels are all good. The choke tubes were sticky so they received some attention as well. All in all, the carbs weren't as bad as I had expected.

I replaced the spark plugs and tested spark. The gas tank was also a mess so I replaced it. The fuel filter and lines were all flushed. The forks are currently out getting repaired and upgraded by one of the members here that I know from another forum.

Here's the issue: The bike will fire, but not run by itself unless the choke is on. It dies immediately when you crack the throttle. In the past I would think the jets/needle area was clogged but I'm not sure. The carbs seated well and hold vacuum. Diaphragms move well while cranking. Fuel spits a little out of the top of the carbs and it wants to backfire. The v boost system is operating normally.

Do I need to pull the carbs again and fully disassemble and rebuild? I was hoping to be able to get past this without pulling three million part carbs apart fully. I've got a new carb sync tool on the way due to my last one being borrowed forever.

Thanks in advance for your time.

 

[tugla]

for sure a sync will help that stumble off idle,but id go back to atleast opening them up,recheck the floats,nothing is clogged in any passage. did you use oem parts/gaskets?

you can visually sync to get them close for start up. all the reg stuff like 2.5 turns on the screw bla bla bla.

just out of curiosity how is the comp on all cylinders?

there are guys here with carbs for sale or can help with a carb rebuild if you need, i know you said its not foreign to you but if you didnt have time.

what are the jets in there also are all the paj1,2 stock? any dyno jet kits by any chance/drilled slides etc?


running with only choke maybe blocked idle circuit,float height too low,too small of a jet? im just thinking out loud here

 

[CaptainKyle]

Pull them back off and pull the jetblocks out and clean them good and make sure the jet block rubber plugs are still soft and not hard as a rock. Your idle circuit is still plugged.make sure you remove your af screws total that needs to be thouroly cleaned.

 

[tugla]

and id make sure use oem gaskets under the jet block for sure

 

[[email protected]]

+1 to the captain.
Carbs need to be totally torn down. The pilot jets in the jet block are notorious for being plugged up. If you are using a cheap rebuild kit beware of the parts.

Check the slide diaphragms as well as the coasting enrichener diaphragms. They tend to shrivel, deform, develop pinholes, or start to disintegrate.

If carbs and airbox are basically stock the vent tubes need to be routed properly.

Check rubber boots from airbox to carbs, carbs to intake, and vboost assembly. Make sure none are dried and there are no cracks.

 

[one2dmax]

Pilot jets are plugged as has already been noted. It's the smallest orifice in the carb (#37.5). When they are plugged the bike will only run with the choke on (which isn't a choke by the way). You are putting fuel into the bike with the choke since it's an enrichener.

Sean

 

[SpecOps13]

Ditto to all the above. Run Real Gas when you're done cleaning the carbs and etc, not Ethanol.. Huge difference....

BTW: Merry Christmas and welcome to the forum...

 

[Meister]

Thanks all! Will pull them back off and fully disassemble.

 

[one2dmax]

Just split it into two pairs. That will allow access to the bowl (and jet block within). The float settings are described on here and pics are on our websites (facebook and regular site). Clear the jets, set the floats, and put it back together.

Sean

 

[Meister]

Rebuild is done with OEM parts, fuel levels set per instructions here and I received a great instructional video form a member (Thanks!). She's running great off idle, but spitting and backfiring upon decel and idle. I'm looking for a vacuum leak but to no avail. I'm missing the 4 vent hoses from the bowls to the airbox, is this a serious issue? Other than that, it went together wonderfully. Drives great off idle and has plenty of power.

 

[one2dmax]

Put the hoses on as that does effect the way the carbs will run. Might have a bad enrichener diaphragm causing the backfire.

 

[Meister]

Put the hoses on as that does effect the way the carbs will run. Might have a bad enrichener diaphragm causing the backfire.

I'm going to check the plugs tonight and see what's going on there. I'd REALLY hate to take those carbs off again.

 

[one2dmax]

The vent hoses are on top of the carbs and only would need the box taken off. If it's idling well then the biggest issue is probably taken care of (plugged pilot jets).

 

[Meister]

The vent hoses are on top of the carbs and only would need the box taken off. If it's idling well then the biggest issue is probably taken care of (plugged pilot jets).

Yes, I replaced the rubber plugs and cleaned the internal jetblock parts in an aircraft grade ultrasonic cleaner. Everything was in bad shape. All the small jets were clogged and the center jets were in pretty rough shape. The caps had disintegrated and cause the biggest issue. Some genius had tried his hand at using RTV black as a plug on one of pilot jet cavities. It was pretty much snot sucked into the jet when I got it out.

Another issue I'm having is that the idle will move around a bit when riding. It will rev to 3k for a while then fail to idle minutes later when I adjust it down to 1500. Temp is the same on the motor. I'm guessing that would also be and enrichment diaphragm issue?

Carbs are seated properly, vacuum is good on all cylinders, the sync is perfect and the sync tubes are safety wired to ensure no leaks are present.

Thanks for all your help!

 

[naughtyG]

Just checking, you did clean/remove/check all four pilot screws, replace their o-rings and have all four with theirs spring, washer and o-ring?

Also, the little o-rings under each diaphragm are all in place?

 

[Meister]

I replaced the hoses and checked the Plugs. Turns out my little "helper" dropped a plug and reset the gap for me after I had them all set. Once it was reset it was all good. It seems to run a little rich on the low end, but the left rear cylinder is running lean. Not sure what to do about this. Going to peruse the rebuild thread and see what is offered on the subject there.

I did ride it a bit over the last week. The '94 now has 7k miles on it! lol