I need jetting help.. Jetting guru's?

[jasonp]

Here we go.
Checked for air leaks. Good to go and even used some Av gasket maker between the manifolds. Here's my problem.
I am adjusting my idle circuit. So on the pilot jet, screw and air jet. I rev the engine up to about 1800 rpm or so and turn the pilot screw all the way in. Then slow back it out tell I get maxium rpms until the engine starts to miss through the exhaust. I come with about 2 1/2 turns out on the pilot screw. So good right.. well now if you rev it up and let off the throttle.. she back fires and cracks through the exhaust like it's lean. So I adjust the screw out half a turn it gets a little better but not perfect... I try more 3 1/2 turns out still no better. ****!! Now I have to change an air jet or pilot jet. . . but now isn't my low speed setting is off. I wonder if I have an exhaust leak? Also it will not start on the choke. You have to just pump the throttle a couple of times and then the engine will fire. Also when it warms up it seems like it doesn't want to start at all. Help I'm sick of this.
Also the accelerator pump is lean. And there is no way to adjust the actual jet or nozzle. You can only adjust the duration of it. Both stoping and starting. If you give the rod a big push when you wack the throttle then the bike just snaps and the engine revs awesome. No matter how soon I start it, the engine will booog for a second then take off. So I guess I'll have to drill the nozzle out a little at a time.
So this carb has been a real pain in my ass. Obvously I'm going to get ripped on because this is why you all went to the brock carbs. I can see why now. This carb does perform when you get it tuned right, it's just a big bitch trying. I think tomorrow I'm going to bring it to the shop and soak it in carb cleaner and the hot water wash it and see if that helps.
Any help would be great here would be great!?

 

[palerider]

A couple of questions.

You say you rev your engine up then adjust your air screw? Unless I misunderstood you. You should be adjusting the air screw with the bike at idle not while revving it.

Also you said it pops after you let it off after revving it up. Again when you rev it up, you are no longer running off of the pilot jet. after you crack the throttle it will transend to the needle and as you open the throttle up more it will be the main jet.

When diagnosing jetting with open throttle you really need to have the engine under a load, trying to diagnose jetting on a free wheeling engine will not net the same results as when the engine has a load on it.

 

[dswwarrior350]

The pilot jet being lean will cause a backfire when you let off the throttle. Id say step up one size on the pilot and adjust the airscrew accordingly.

I cant say for sure... id have to see it in person.

However adjust the needle up one click also will affect the 1/3 throttle position slightly.. I guess the best advice i can give you in just to try adjusting some things and change out some jets.

 

[jasonp]

A couple of questions.

You say you rev your engine up then adjust your air screw? Unless I misunderstood you. You should be adjusting the air screw with the bike at idle not while revving it.

Also you said it pops after you let it off after revving it up. Again when you rev it up, you are no longer running off of the pilot jet. after you crack the throttle it will transend to the needle and as you open the throttle up more it will be the main jet.

When diagnosing jetting with open throttle you really need to have the engine under a load, trying to diagnose jetting on a free wheeling engine will not net the same results as when the engine has a load on it.

Yes you turn you idle screw up or hold the throttle at somewhere less then a quarter throttle to adjust the pilot screw. You want your rpms around 2000. This is pretty standard in just about every tuning book I've read and online. You don't want to adjust it at idle.
When your on the idle circuit then how are you going to put load on? You want me to drive it around and see how it idles? Same for the accel pump. It does the same thing under load. It boogs. Your on the pilot jets when you have the throttle off.. aren't you? So when your engine is coming off rpm and you have the throttle closed what circuit are you on? It's not hard to figure out. That's why I said I'm lean on that circuit.

 

[jasonp]

The pilot jet being lean will cause a backfire when you let off the throttle. Id say step up one size on the pilot and adjust the airscrew accordingly.

I cant say for sure... id have to see it in person.

However adjust the needle up one click also will affect the 1/3 throttle position slightly.. I guess the best advice i can give you in just to try adjusting some things and change out some jets.

No ds.. Airscrews are on two strokes! 4 strokes have pilot screws. In the 1/4 to 3/4 throttle it runs rich.

 

[griff]

If I read your sig correctly, this is the flat slide carb?

If you are free-rev'ing the engine trying to determine your jetting, youre not going to get anywhere quickly. Tuning flat slides is a PITA in general.

At this point, just get your idle set as best you can, then take it for a spin. You need a load on the engine to tune properly.

Get into second gear, rolling just above idle, and SLOWLY wind the throttle up. If its bogging, then too rich - choking (choppy lurching), then too lean.

Based on how far you are open on the throttle and the reaction you get at a particular throttle opening, you should be able to narrow down which circuit that needs tweaking, pilot > needle > main.

If you can get that cleaned up, THEN tweaking the pump is the next step to fine tune it.

Of course, this assumes youve taken care of any exhaust and/or intake leaks you might have

 

[palerider]

Yes you turn you idle screw up or hold the throttle at somewhere less then a quarter throttle to adjust the pilot screw. You want your rpms around 2000. This is pretty standard in just about every tuning book I've read and online. You don't want to adjust it at idle.
When your on the idle circuit then how are you going to put load on? You want me to drive it around and see how it idles? Same for the accel pump. It does the same thing under load. It boogs. Your on the pilot jets when you have the throttle off.. aren't you? So when your engine is coming off rpm and you have the throttle closed what circuit are you on? It's not hard to figure out. That's why I said I'm lean on that circuit.

You come on here and ask for help. Two people take the time to offer help and the only thing you do is condescend them. It is about impossible to jet a carb over the internet without being there to hear what it is doing ourselves and are just offering help. If you do not agree with us then fine. You are the one that asked for help, not us.

Good luck getting someone else to take the time to help you with a problem since you obviously ******* know everything. So my final opinion is I could not give a **** less if you ever get it running and your sig is right you are quite the ******* ass klown.

 

[dswwarrior350]

[quote:y4yn6qpt]The pilot jet being lean will cause a backfire when you let off the throttle. Id say step up one size on the pilot and adjust the airscrew accordingly.

I cant say for sure... id have to see it in person.

However adjust the needle up one click also will affect the 1/3 throttle position slightly.. I guess the best advice i can give you in just to try adjusting some things and change out some jets.

No ds.. Airscrews are on two strokes! 4 strokes have pilot screws. In the 1/4 to 3/4 throttle it runs rich.[/quote:y4yn6qpt]


: You knew what i meant, holy crap.

Move the clip up one notch on the needle.


Your main jet can play some head games with you depending on the carb design. I dont really know what carb you have. I know that on certain models the main jet can start to come in as early as 1/2 throttle. But thats beside the point. If your carb has a needle, then move the clip like i said and that should lean you up a little bit in the midrange, if it needs more then move the clip again. The pilot most likely needs changed if you can't compensate for the jetting with just adjusting the PILOT screw (ive always called it pilot/airscrew). Go up one size on the pilot and then adjust the the PILOT screw in.

And yes despite your advanced knowledge in order to make sure the machine is running right you must test ride it after each change. It states that right in the front of my edelbrock manual and at each section about each adjustment. Even the pilot jet, riding it can tell you more than enough about your adjustments if you know what to look for.

Just some guidelines

Things to look for on your test ride

LEAN CONDITION:
1. Hard starting
2. Flat spot in acceleration off idle
3. Lag in acceleration
4. Popping or backfiring through exhaust on deacceleration
5. Erratic inconsistant idle

Leaks can also cause those but you said you checked all that so no need to mention it.

RICH CONDITION
1. Black smoke at idle
2. Lazy acceleration
3. Poor fuel economy
4. Surge at low speeds
5. Rough idling


MIDRANGE TO FULL

LEAN
1. Will not rev out in higher RPMS
2. Poor acceleration when throttle is rolled on at higher rpms
3. Detonation and pinging

RICH
1. Black smoke from exhaust at high RPMS.
2. Lazy acceleration
3. Power falls off at wide open throttle and accelerates when throttle is rolled on closed slightly



The accelerator pump works everytime the throttle is moved ,without it the motor wouldnt really be able to compensate for throttle changes well especially abrupt ones.

Too small of a pump shot will cause a stall or stumble during quick throttle openings

Too much will cause it to be sluggish but then it will clean out and run normally

This is one adjustment that can only be tested by riding the machine, without a load on the motor you will never know how it responds to the pump shot unless you are way to far in either direction.


And with all this said another thing that could be throwing jetting off could be your float level.

 

[jasonp]

It was the pilot screw. The needle of it broke off inside the carb and was stuck. I must have seated it to hard.

 

[jasonp]

You come on here and ask for help. Two people take the time to offer help and the only thing you do is condescend them. It is about impossible to jet a carb over the internet without being there to hear what it is doing ourselves and are just offering help. If you do not agree with us then fine. You are the one that asked for help, not us.

Good luck getting someone else to take the time to help you with a problem since you obviously ******* know everything. So my final opinion is I could not give a **** less if you ever get it running and your sig is right you are quite the ******* ass klown.

hahahahahah
How is asking questions condescending? Thanks for your "opinion" it really means alot, honestly.

 

[jasonp]

you where right ds... the float was off as well. Thanks for the post with the brock stuff!

 

[jasonp]

**** ds I've always called it a pilot screw and when I seen air screw.. I'm like well I have a air jet?! Maybe he means air jet.. I know you can change the air jet and just about does the same thing as the pilot jet... but smaller on the air jet is richer where smaller on the pilot is leaner.

 

[griff]

It was the pilot screw. The needle of it broke off inside the carb and was stuck. I must have seated it to hard.

Hehe, broken parts will certainly make tuning more difficult!

 

[jasonp]

agreed!! haha I've always used my finders to seat the screw so everyone be careful when closing the pilot all the way.
Hey Griff can you explain something to me? Why is it that with this flat slide carb that my jetting is around a 120 on the main jet and with my other cv carb the main jet was around 145? Is that a better design or something?

 

[griff]

Better? Not really, just different approach. CV carbs and Flat slides are two totally different animals when it comes to "fuel delivery". Its just the difference in fuel circuit design, float bowl capacity, then add the acc' pump into the equation, etc etc etc.

Its not unusual to see a vast difference in main size like you noticed.

Another factor people dont think about is vacuum signal from the engine. Displacement, CR, cam choice, play a part in that.

For example, my Bandit 1200 uses 152.5 mains with stock cams, pistons. A very common config. Now, a lot of guys will go farther, and change one or both of the cams, over bore and/or high CR pistons, and find that 152.5 is now too rich, and they actually have to go down a couple sizes on the main. The reason is that the engine now has a substantially stronger vacuum signal on the intake stroke (mostly because of the new cams), and actually pulls too much fuel from the carb at one time. The only way to meter it is to go down on the main to restrict the flow a little so the a/f ratio comes back to normal.

 

[jasonp]

Interesting! In school we talked about how more compression actually uses less fuel (BSFC) because there is less area for the air fuel charge. It was always really hard for me to grasp that because in the other sense your also making more power. So more air.. more fuel.. more power.
I know when I bought this carb the big selling point was the design of the carb promoted more vacuum to the circuts or jets which made the jetting more percise. I guess that also plays a roll?

 

[dswwarrior350]

you where right ds... the float was off as well. Thanks for the post with the brock stuff!

No problem.. happy to help!