Sputters at about 1/4 throttle

Sorry for all the questions, but even after reading about carbs, they still scare me a bit!

I am using the stock airbox and have a 4 into 1 exhaust and have stock jetting. All the passages in the carb are clean and I have set the fuel level using the clear tube (all my valve clearances and compression are fine as well).

The bike will start right up and I can take it off of chock in a minute or so. The idle then stays at a nice idle at around 1000 rpm. I can rev it and it is very responsive. The issue is when I ride it, it will start to sputter at about 1/4 throttle. It will eventually rev up, but it is not smooth at all. It feels like it is starving for fuel.

Would having the 4 into 1 exhaust require bigger jets? I know using the pods require a rejet, but I thought I read that a rejet is not needed if a pipe is the only modification.

I am just not sure where to go from here. I am very happy that I have it running on all 4 cylinders and idling nicely, but now the tweaking game starts!

I do have a bit of an exhaust leak at the header (I will get a one piece V and H eventually). Will that cause the issue mentioned?

If it will help, I can strap on my GoPro camera and make a video of the issue.

Thanks.

You may want to make sure the timing advancer is operating freely. If it is sticking it can cause symptoms similar to those you describe. I would clean and lube it just to be on the safe side. Ed

You might also experiment with the position of the carb needles. Most bikes the pilot jet regulates the fuel/air below 1/4 throttle, then the needle position takes over up to about 3/4 throttle.

Yeah, the bike has been sitting for years. I will certainly work on the advancer. I should also check the timing with a light.

I am thinking about getting a jet kit, so that will be a good time to play with the needle position.

Thanks for the suggestions.

Hi Mid Life Crisis
I think your carbs are same as mine - Keihin CV34. I have stock airbox and a Mac 4 into 1 exhaust and I have the secondary main jets @ 130. Primary main stock - 62 ? I think (not totally sure) that I have the air mix screws at 2 1/4 turns out from lightly seated. My bike came with pods so I was jetting down when I put the airbox on and cant say for sure how it would have performed with stock jetting and 4 -> 1

Does the stutter start at 1/4 throttle - say about 3000 rpm and continue through increasing rpm or does is just happen at about 1/4 throttle and is ok above that ?

I think those are the same carbs as mine (I will need to check). The sputter seems to start at just under 3000 and continues through when I increase rpm. It seems to clear up for a split second and then sputters again. It is certainly not a smooth transition as you bring up the rpm's.

I will need to check which jets I have. The PO said that it was not jetted (even though he was running the pods), but I guess it is possible that someone before him did something.

Ok

When I got my bike 10 years ago I had a stutter between 2500 and 3000 rpm. Above 3000 it was fine. Drove me nuts and took me an entire summer to figure out. I cleaned the carbs 3 times and swore that all passages were clean but it still ended up being carbs and specifically the transition holes. I'm not sure if that's the correct term. These holes (3) are where the fuel/air from the pilot circuits come together. Patton has a diagram which he has posted many times.

If you have the carbs off the bike then operate the throttle mechanism to open the throttle flaps/butterflies. Look in and up. You will see 1 hole from the air mix screw and behind that 3 tiny holes just where the throttle flap would close. To make sure the holes are clear take a small pin and make a right angle bend near the tip and use that to poke the holes.

Good luck

I just did that today! I read a recent post that mentions those holes, so I made sure they were clear.

These carb issues (if that what they are) drive me nuts. I don't mind doing other difficult jobs on the bike, since you know what you do is going to fix the problem. You can redo these carbs completely and STILL have an issue! I am glad you were able to fix your problem. It gives me the push I need to keep working at it!

Good luck getting it lined out. It's aggravating to have an issue and having to guess at the problem. I just re did my carbs and sprayed carb cleaner through every passage I could find and through all the jets. You can also pull a wire out of a wire brush and run it through all the small holes or strip the paper off a bread tie and use that.

I used a wire from a wire brush, and that did seem to work well. I cleaned the carbs very well, and I am confident that all the passages are clear.

Yep...aggravating is a good word for this!

Check the tower log, er, sorry, advancer like Ed said. Also check voltage to the coils. You might find some long lost power hidden under a voltage drop due to bad connections. Don't start tuning carbs unless everything electrical is good.

Alan

Agreed. I think I am going to freshen up the connections front to back on this bike. It will take some time, but after sitting for so long, it will be worth it.

I hate taking the carbs off, so I will try anything I can before I need to start messing around with them!