Need larger pilot jet?

[MechNewb]

Hey all, hopefully one of you can help me figure this out.

When I bought my bike it was running really rich and had carb problems.
I cleaned the carbs, replaced the float needle, and set the floats to 22 mm (brass floats).

I switched to pods and since it was running rich beforehand, I bumped the main jet up to 135. It originally had 132.5 main jets and 42.5 pilots.

Now I've got it running better, I took it for a ride last night and now it's revving up whenever I pull the clutch in at a stop. I checked today after work and even sitting after just starting, if I rev it a little, it revs up to about 4500 rpm.

I checked and the throttle cable isn't getting caught, it snaps back when I let off. When I start it up cold, I have to play with the throttle to stop it from stalling (partly due to the idle not being set correctly since it won't stay). When I pull the choke out half way, it idles much better, and if I pull it out fully, it seems to want to die again.

I also changed the carb boots to brand new ones so I don't believe it should be an air leak. I'm thinking the pilot jet is possibly too small and causing it to run lean at idle? I've got the mixture screws at 3.5 turns out.

 

[Bizzy13]

What year is it? When you let off the throttle does it decelerate quickly or hover and fall slowly at idle? This problem w/ the idle suddenly going ape shit seems to be a very common problem on these bikes. We need to get to the bottom of the issue! I have this from time to time and I've seen a couple others having it to

 

[MechNewb]

It hovers and stays. When I took it out last night I ended up hitting the kill switch otherwise I would be sitting there in the middle of the street with the bike revving like crazy. It sucks cause before it ran like shit, but now it seems to run quite well except for at idle.

 

[Bizzy13]

It usually indicates a lean condition. Or idle set too high. Are you running pods and open header? And what year? I know the stock jet in mine is 135, but the older ones were a lil smaller.

 

[Scorpio1963]

Seems like it is a common problem,I have owned my bike for a year almost to the day and it has done this on and off ever since I owned it.

 

[Bizzy13]

I'm kind of wondering if everyone having this problem is running pods and oversize jets. For one, these carbs take a certain pod that doesn't block your air jets, and two, I can't help but wonder if its a pilot jet issue. It controls your idle, maybe it needs upped a size or two.

 

[MechNewb]

It's a 79 so as far as a I know, the stock was 132.5. It's got the pods from Mokes which don't block the air. I haven't touched the idle screw cause I haven't been able to get it warmed up and settled enough to set the idle screw. I think in gonna try upping the pilot jet as I've got one on hand and see how that goes. The mufflers are big Harley ones that came on it when I bought it.

 

[Bizzy13]

Yea that's right for that year. Id try screwing that idle screw out a little bit bro. It may just be turned in to far. Turn it out till its just touching the throttle, then screw in 2 turns and start it @ half choke. When it starts to speed up let the choke out if its fast or slow just adjust the idle screw in or out. Once you get it idling at a goo rpm rev it a couple time and let off, see if it comes back down or stays up.

 

[MechNewb]

Yeah I'll mess with it a bit more before I take the carbs off again. It idles at about 1200 when I first get it started but it's once I rev it a bit that it stays up at around 4-4.5k rpm.

 

[Bizzy13]

Mine was decelerating real slow at idle when I revved it at first. It hovered and dropped slowly. I cleaned the carbs and turned my mixture screws out from 2 1/2 turns to 3. It stopped doing that and now drops immediately.

 

[Bizzy13]

Since it runs better when you're at half choke it just points more toward you being way lean.

 

[frwinks]

I cleaned the carbs, replaced the float needle, and set the floats to 22 mm (brass floats).

The correct height for brass floats is 27.3mm +/- 1mm

Start with 3 turns on the fuel mix screw, if it still hangs or drops slowly, keep turning it 3.25, 3.5 turns...etc Anything over 3.5 turns go up on the pilot

 

[Bizzy13]

^ yup, 1/4 turn at a time. Thanks frwinks, I didnt know that about how to tell when you need a bigger pilot. although pilot controls idle, main is higher rpm. My mixture actually run best around 2 1/2. But keep playing w/ it.

 

[16VGTIDave]

With these carbs, all the jets overlap. The trick to tuning the jets is to start with the main jets, get them right for full throttle high RPM operation. Then get the needles adjusted for full throttle mid RPM. Then the pilot jets can be adjusted for part throttle cruising and hard acceleration from 2000 RPM. If the pilot jets are either too rich or lean because of the 2.5 sizing increments, the float levels can be adjusted to get it right. Finally, the pilot screws can be adjusted for a good idle.

Obviously, valve adjustment and the ignition system have to be good or the numerous test rides and adjustments will be wasted. And make only one change at a time while keeping detailed notes or you will be chasing your tail...

 

[MechNewb]

Yeah sorry, they were originally set to 22 mm when I originally had problems but then I adjusted them to 26 mm when I replaced the float needle. Sorry about that.

I'll be playing with the bike this week and I'll report back with what I find out solves this problem. I'll try to keep a log of what adjustments I make and the affects. Hopefully this can help someone else with this problem.

I'll check the points and valve adjustment this weekend to make sure as well. Thanks for the help everyone.

 

[xschris]

With carbs that have the idle mix screws exposed make sure the tips of the needles have not broken off in the carbs it is very common for this to happen in these models (77-79)

 

[MechNewb]

So I figured if I was going to solve this thing, I had to rule out all other possible problem areas. So this weekend I checked the valve clearance, gapped the points, checked the spark plug gap and made a manometer. I'll hopefully be making some How tos in the next couple days for the site. I also lubed the throttle cable.

My point gap on the right side was super small and not big enough so I adjusted that. The valves were all within spec though.

I started it up and synced the carbs using the manometer. It doesn't seem to have the hovering idle problem it had before so I'm thinking that problem might be solved,but now the right cylinder is running nicely but the left cylinder is slightly popping at idle. When I rev it though, it sounds good. I didn't get a chance to test ride it though as it got too dark and with my license I can't ride in the dark so that'll have to wait till tomorrow. Hopefully I can get it solved tomorrow.

 

[MechNewb]

After researching a bit, it seems that the popping is caused by a lean mixture. This makes sense as the left cylinder was colder to the touch than the right side. I had the mixture screws turned out four turns so I think it's time to go up one size on the pilots. I'll confirm this tomorrow.

 

[Scorpio1963]

Yeah I'll mess with it a bit more before I take the carbs off again. It idles at about 1200 when I first get it started but it's once I rev it a bit that it stays up at around 4-4.5k rpm.

I fixed this problem by adjusting the screw from undernieth the carbs.Then I played with the idle screw till I got to idle at 11k.My mains are 2 and half sizes up with the pilot up one size.I have air mix screws at 3 and quarter turns.When I rev it up to about 3-4k the idle drops back real quick and stays at 12k.Once you get tuned in half way decent then sync the carbs your problem will be taken care of.Also like bizzy says check for vacume leaks and tryed to eliminate them.This was part of my problem.