carb #4 rich VM 26

[jknappsax]

I rode the other day, and everything seemed pretty good, except when I would goose the throttle, the RPM would go up, then hang at about 2.5-3K for about 10 seconds. I've been meaning adjust mixture with my Colortunes, so after I rode, I mounted the Colortunes, and all the carbs were a little rich, but adjusted in fine, EXCEPT carb #4, which is consistently rich, even with the fuel screw adjusted lightly seated. I could adjust the air screw and bring down the richness, but it's screwed almost all the way out. I'm planning on pulling the carbs, which have been dipped and rebuilt, but I'm trying to figure out what might cause this. As far as I know, the idle jets are all the same, and I had installed a Stage III jet kit in each carb, fiddled with needle heights until all seemed to be running pretty well. I'm sure that the floats are set to the right height (though I will doublecheck carb #4). Any other thoughts on what I might be on the lookout for?

[rustybronco]

I rode the other day, and everything seemed pretty good, except when I would goose the throttle, the RPM would go up, then hang at about 2.5-3K for about 10 seconds.

I'm sure that the floats are set to the right height (though I will doublecheck carb #4). Any other thoughts on what I might be on the lookout for?

I'm not so sure the float levels are set correctly. before you pull those carbs, check the wet fuel levels with a piece of clear plastic tubing, held near the float bowls.

there are a lot of thing that can contribute to an incorrect fuel mixture on your# 4 carb, such as a damaged needle and seat, a held open choke plunger, or a damaged seating surface on the plunger, in addition to an incorrect fuel level.

in regards to your issue with hanging at 2.5-3k rpms, I believe you might still be a little lean on the needles. so, after you correct the issue with #4, read those plugs and do what they are telling you.

[tkent02]

I rode the other day, and everything seemed pretty good, except when I would goose the throttle, the RPM would go up, then hang at about 2.5-3K for about 10 seconds. I've been meaning adjust mixture with my Colortunes, so after I rode, I mounted the Colortunes, and all the carbs were a little rich, but adjusted in fine, EXCEPT carb #4, which is consistently rich, even with the fuel screw adjusted lightly seated. I could adjust the air screw and bring down the richness, but it's screwed almost all the way out. I'm planning on pulling the carbs, which have been dipped and rebuilt, but I'm trying to figure out what might cause this. As far as I know, the idle jets are all the same, and I had installed a Stage III jet kit in each carb, fiddled with needle heights until all seemed to be running pretty well. I'm sure that the floats are set to the right height (though I will doublecheck carb #4). Any other thoughts on what I might be on the lookout for?

You have a stage three kit, do you have the pipes and pods to go with stage three?
Has it ever run perfectly with this kit installed?
Look at the fuel level while the engine is running, it may be high causing richness on #4 for whatever reason.
That may or may not be the cause of the way it is running, likely three cylinders running properly would get the RPM right on up through the 2.5 - 3k range, even with one not working so well.

[jknappsax]

The bike came with K&N pods and headers; the PO told me the Stage III kit had been installed, but it never was. after adjusting the valves, timing the bike, syncing the carbs, I'm on to the tuning. It is running better than it ever has, but I'm working out the kinks as I find them. I'm pretty sure that the float height is right, and the metering needle and seat are new, as were the needles (to the DJ adjustables) as well as all o-rings, etc. I'll doublecheck everything on this carb. Thanks.

[Coady]

I'm not so sure the float levels are set correctly. before you pull those carbs, check the wet fuel levels with a piece of clear plastic tubing, held near the float bowls.

there are a lot of thing that can contribute to an incorrect fuel mixture on your# 4 carb, such as a damaged needle and seat, a held open choke plunger, or a damaged seating surface on the plunger, in addition to an incorrect fuel level.

in regards to your issue with hanging at 2.5-3k rpms, I believe you might still be a little lean on the needles. so, after you correct the issue with #4, read those plugs and do what they are telling you.

Everything here is good advice and the jet needles being lean rings true too. Checking the fuel level with clear tubing will definitely rule out the fuel needle and seat and float level - then you can go from there.

[jknappsax]

As to the needles, I figure I should either move the e-clip to the next lower slot (so the needle is further out of the main jet for a particular throttle setting) or remove the spacers on top of the clip and substitute washers so that the needle is also a little further up out of the main jet. Am I visualizing this right? Or does anyone have any other advice. TIA.

[TheCafeKid]

Are you using dynojet jets? I've read where people have had problems with MiC jets and DJ needles. Anyway to richen the needle circuit the clip should be moved down on the needle. This will set the needle higher in the needle jet and quicken the speed at which fuel is delivered throughout the length of the circuit. To lean it out the clip moves up on the needle. To get a half clip movement you will need TWO washers of the same size as the ones included with the needles. Those will go under the large nylon spacer and above the clip. Two washers are one half clip position. Do not remove the nylon spacer. The DJ needles and washers should provide you with pleanty of adjustment range provided your mains are the correct size. If on number four with the air screw is open all the way ( remember that turning the air screw
out will lean the pilot circuit. You may need to go as many as two or three turns OUT) it's sill too rich and you're positive both the fuel level is correct AND the float itself is not taking on fuel, check your fuel screw setting.

[jknappsax]

I'm using both DJ needles and main jets. I got 4 of each 138DJ and 142DJ, installed the 138s. On carb #4, I lightly bottomed the fuel screw, and it did not lean out the mixture adequately. When I say I had to turn the air screw out a lot, I mean A LOT! It was screwed almost completely out. I need to revisit the float level, but they were all set identically at 23mm. The only way I'll know for sure what is going on is to pull the carbs and get a good eyeball on carb #4. I appreciate all the advice. Thanks. I'm just thisclose to having the tuning right; the other 3 carbs look right on with the Colortune, and I just want to RIDE a lot before we get snow.

[KEITH KRAUSE]

As to the needles, I figure I should either move the e-clip to the next lower slot (so the needle is further out of the main jet for a particular throttle setting) or remove the spacers on top of the clip and substitute washers so that the needle is also a little further up out of the main jet. Am I visualizing this right? Or does anyone have any other advice. TIA.

Don't remove any factory plastic spacers or install them in a different order.
If your 1/3 to 1/2 throttle position test runs showed lean plugs, then richen the jet needle by lowering the e-clip position. How much depends on test results. If the plugs were very white then more than 1 position richer is most likely needed.
The 138 DJ mains are the most common choice for quality pods/pipe.
You must bench synch carefully and then vacuum synch before accurately re-jetting. The vacuum must be reasonably matched to run correctly and judge the jetting.
As a common starting point, set the pilot fuel screws underneath to 1 1/4 turns out and go from there. Test at minimal throttle position to fine tune the pilot circuit. They are intended as fine tuning for the pilot jet.
Set the side air screws to 1 3/4 and then adjust using the highest rpm method. Once set and the bike is warmed up fully, vacuum synch.
If the carb is clean, float level set at approx' .95", and no worn parts such as needle jet/float valve, etc, vacuum synched closely to other carbs, then it shouldn't be richer than the others.
Also, remove the floatbowl vent lines and leave the ports open. This helps eliminate fuel starvation when running pods on your model.