Question on Main Jet

[buck1974]

I have a questions that might be dumb one, but asking anyway. I recently had an issue with my bike coughing/sneezing at highway speeds of about 70 at 2750 to 3000 RPM. I read the S&S guide and upped the Inter jet two times to a 33 and Im still out about 5 turns on my adjustment, however my main is a 76 and I have yet to change it. My questions is I can obviously tell when the ( Inter ) Jet needs to be upped, but what symptoms would you have with the Main besides checking the plugs. It seems to feel ok, but could it be better and me not know it. What are the symptoms of a Main Jet being to small.

 

[BadBrad]

I have a questions that might be dumb one, but asking anyway. I recently had an issue with my bike coughing/sneezing at highway speeds of about 70 at 2750 to 3000 RPM. I read the S&S guide and upped the Inter jet two times to a 33 and Im still out about 5 turns on my adjustment, however my main is a 76 and I have yet to change it. My questions is I can obviously tell when the ( Inter ) Jet needs to be upped, but what symptoms would you have with the Main besides checking the plugs. It seems to feel ok, but could it be better and me not know it. What are the symptoms of a Main Jet being to small.

That's a damn good question Buck that I don't have the answer to, but I'm sure there are some here that have the answer. My reply is to tell you that I'm running a stock pitbull/117 in south MS and south LA with a 78/33 jet combination. I had the same "cough" and it drove me crazy. I had a 76/31 in mine when I had the problems. Raywood told me (after I had already changed them) that changing the main jet air bleed will also give similar results.

 

[Staffy]

If you have not read this - PLEASE DO SO
http://www.bigdogbiker.com/forums/how/4943-how-adjust-your-carb-check-jetting.html

BEFORE doing anything crazy check your air/fuel mixture screw, pull it all the way out and make sure it has no signs of damage - this can cause symptoms you are describing.

Rule of thumb - more than 2.5 turns up one size on the int.

Do post your setup, your location, pipes and filter, also any engine mods - that will help as in giving you a base line to work with.
Good luck - keep us updated.

 

[V]

I have a questions that might be dumb one, but asking anyway. I recently had an issue with my bike coughing/sneezing at highway speeds of about 70 at 2750 to 3000 RPM. I read the S&S guide and upped the Inter jet two times to a 33 and Im still out about 5 turns on my adjustment, however my main is a 76 and I have yet to change it. My questions is I can obviously tell when the ( Inter ) Jet needs to be upped, but what symptoms would you have with the Main besides checking the plugs. It seems to feel ok, but could it be better and me not know it. What are the symptoms of a Main Jet being to small.

The idle mixture screw being out 5 turns is indicating something else. Wiith the bike hot at idle turn the screw in slowly until engine starts to pull down then back it out again unitl is smooth idle. Idle should be between 950-1050 RPMS. Less and the tach will start to flash. Might try a 78 main and see how that does. You can do the main from the bottom of the bowl drain plug with out removing everything if you're carefull. There is also a .040 Air Bleed in the carb that can be changed but you will nedd to remove the bowl for this. Alot of people have stepped up to a larger air blled to smooth out the transition from the intermediate to the main jet which is around 2500- 3000 RPM. I'm runnning a.590 cam with .33 intermediate and .78 main. Stock .40 air bleed

Now somebody who knows whats up correct me on this stuff! :lol:

V

 

[demo man]

my bike is doing the same thing and it's drivin me nuts! i'm sick of playing with the jets, as soon as i get it runnin good i decide to change something and it's back to the drawing board. i ordered a PSI carb and i'm hoping it cures any future problems.
tim

 

[Raywood]

Just my opinion but what Buck is describing is a over-rich problem at the transition period. I guarantee you that if you call Bob at Triple X he is going to tell you to open up your air-bleed. The air bleed controls when the main jet comes on. Bigger delays its.

If it was lean it would start back firing or sounding like it's out of gas!

Another thing is stock jets on a new 117 with the BR pipes is 31/76. Anything larger your just ruining your around town tuning. You spend what???? 50% 75% or more in you intermediate jet so don't fuck up your everyday street riding by raising the intermediate trying to fix an issue at 3000 rpm when it's not the problem.

Another thing is air-cleaner and pipes, they all play a role in tuning. But to know the real story you need to have an exhaust analyzer to give you the true story.

Just my 2 cents.

 

[buck1974]

Raywood, I have been thinking along those same lines, However I did not post what I have added to my bike. I have the Big Radius pipes 2 into 2, and a S&S dual Runner, CM612 Cam. My thought was why am I continously going up on my inter. jet and not touching my main. Raywood I'm going to research more of your thoughts and go that route and update what happens. Thanks for the info.

 

[avdhunter]

Buck what Ray is telling you for the most part seems right on as far as the air bleed. I have a phsycotic air cleaner on mine and had a hell of a time getting mine dialed in. My carb has a fixed air bleed so wasn't able to change it (without drilling). The coughing and stumbling that you describe is exactly what my bike was doing when it was leaning out just before the transition to the main jet. If you adjust the air bleed you can have it come in sooner which will get rid of the leaning out.... but your highway milage will probably suffer from it!!!! Contrary to the norm of what people run around here.... I wound up with a 33/78 combination on my internally stock 107". With that combo I have no problems unless I am pulling a hill @ 75-80 MPH then it will start hesitating a little bit. I had went up to a 35/80 but it was too much (too rich)for running around town. I am not sure how the S&S Dual runner is set up but if it is set up in a way that the faster you are going the more air gets forced into it with no-way to escape or by-pass... you will have to find a way to let it bypass or get as close as you can on the adjustments and then live with em. Oh and I am still getting 52MPG with my 33/78 setup. Hope this helps Bro!!!

 

[buck1974]

Thanks for the replys, they have been very helpful, I just have one other question? Say if I do open up the air bleed abit, and I'm happy with the setup I have. Then on down the road I want to upgrade to a XXX carb, would I see a big difference upgrading to that if its running great? Also if I did go to the XXX carb, it isn't a bolt on and go process, will I have to go through all that I have with tuning this carb as well. Buying jets testing asking this and that?

 

[stlmikie]

Nope.

Thanks for the replys, they have been very helpful, I just have one other question? Say if I do open up the air bleed abit, and I'm happy with the setup I have. Then on down the road I want to upgrade to a XXX carb, would I see a big difference upgrading to that if its running great? Also if I did go to the XXX carb, it isn't a bolt on and go process, will I have to go through all that I have with tuning this carb as well. Buying jets testing asking this and that?

 

[buck1974]

Mike are you saying that I wouldn't see a difference, or its not a bolt on and go process without adjusting the jets on the XXX carb?

 

[buck1974]

I'm thinking about calling Bob in the morning at XXX carbs, for those of you who have the xxx carb, is it a bolt on and go process, or is it back at the drawing board with figuring out the right jets and such?

 

[Raywood]

I'm thinking about calling Bob in the morning at XXX carbs, for those of you who have the xxx carb, is it a bolt on and go process, or is it back at the drawing board with figuring out the right jets and such?

Bob does a great job of setting it up for you region you live in. If you think you can install it and run down the road then no. Even your stock model had to be adjusted. To many variables like intake, exhaust and more.

But he gets it close. Learn to adjust your carb, download the file from the S&S site. It's a very easy carb to work on.

Good luck

:2thumbs::2thumbs:

 

[buck1974]

I live in the South East, Alabama

 

[buck1974]

Also I was thinking of the XXX carbs, however I see the Taz ones, any experience with those? The money difference is it worth it to get the TAZ over the other xxx carb that is offered.

 

[stlmikie]

Just get the psi. You'll love it.