Runnin crappy when hot

[audijunky]

Went on a long ride over the weekend. Skyline drive in VA down to Roanoke for the mid east members. BIke starts to sputter and backfire real bad when it gets hot. I think it might be runnin rich, but when I got my carbs synced (before the ride) the plugs showed I was running lean. before the sync I had been runnin for about an hour on the freeway around 5k rpms. So the mech ( my buddy) backed out the mix screws 2 full turns. I checked my plugs before the long trip and they looked a liitle rich but have'nt yet after. During the ride I turned them in a 1/4 turn with no effect. Also when I start it in the morning I only need the choke for about 30-45 sec. Backgroud: 79 standard, pod filters with TC's velocity stacks, open header with washer inserts for back pressure, inline fuel filters, 145 main jets, 45 pilots.
Question: could two turns out on the mix screw take you from lean to rich( one end of the spectrum to the other)?
Any one got any suggestions?
As soon as I can find a pair of cheap mufflers I am gonna put them on and see what happens. But until then what do you think rich or lean when warmed up/ hot.
Thanks for your help

[79XS11F]

Not likely from one end to the other but they do affect the entire range. The engine could still be running lean and getting hot or one or more ignition components may be acting up when they get HOT.
I would check for spark at all plugs as soon as this issue appears and if they are good check jetting, air leaks at boots or exhaust
Rob

[AlanB]

Hi Audi,

Perfectly possible to be rich on pilots and lean on main jets, or the other way round, especially when things are as far from stock as yours!

Don't assume the problem is the same all through; treat each end as it feels!

I should really post a couple of pics of my cars for you; probably in the "other bikes" forum....... I have added a black (all aluminium!!) Audi A2 turbo diesel 75 to the Audi 200 (5000?) Turbo quattro Avant.

AlanB

[audijunky]

Sound like yo have some nice cages there Alan!! I have a 2000 A6 Avant Wagon. No turbo its the 2.8 litre 30 valve V6.

I thought that the idle circuit affects the main circuit. from the looks of the fuel/air flow diagrams I have seen on here, the pilot circuit does not completely shut off when you reach higher RPM's.
I have purchased 147.5 pilots and 150 mains. What is the cheapest way to figure out if I am rich or lean for both circuits? Spark Plugs? Buy two new sets and run it at low RPMs (for how long?) too see how the pilot cicuit is running and then do the same at high RPM's with diff. plugs?

[AlanB]

Hi Audi,

The circuits all affect one another, but that still does not mean that the problem wil be the same all through.

I am pretty sure there are good instructions on here for how to do Plug Chops, and for the best order in which to adjust the circuits, so no point in me doing it all again. I am sure someone more experienced than me will be able to find a link?
However, If you are still running long open pipes(no baffling!) and no air-box, you may need some strange settings to get it running right.

I guess you know about my solution to the problem?

CLICK HERE!

Best of luck!

AlanB

[petejw]

Hi Audi,
the best and quickest way to check the fuel circuits
if there running rich or lean.
ride the bike, if it runs better when its cold, its running rich,
if it runs better when its hot its running lean, the bike should
perform pretty much the same when its warm or cold, do the
check at different speeds/ throttle openings for each of the circuits.
the pilot jets do come into affect with the mains under light throttle high revs.

btw 2 full turns on the pilots will make a big difference to the pilot circuit.

[TADracer]

My mods are similar to yours and I am at 145 mains and 45 pilot jets, needles in the mid setting (stock) and idle is perfect at1 1/2 turns out. These work perfect for my machine throughout the whole RPM range.

Reading the plugs is not the do-all, end-all. Besides, it takes about 15 minutes of riding at a constant throttle and load to significantly change the insulator tip color. So, if you are rich today and change to smaller jets then take a spin around the neighborhood, your plugs may still read the same. If you are not sure about your jetting, tune from the top down. It is not that hard to do and takes away all the guesswork because you are tuning each carburetor circuit individually.

There is an article called Tuning CV Carbs (not sure where the link is here but maybe one of the gurus will know) that explains exactly how to do it.....and it works. First, you pick the best main jet by choosing the one that pulls hardest up to the redline, then the best needle setting, then the best pilot jet by accelerating hard in high gears from slow speeds, then the best setting for your idle mixture screws. Once you find the combo, this is the baseline for your setup.

You will be amazed at the added performance and rideability when you hit the combo right.

[petejw]

I think this is the link that tadracer is talking about

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

this is the info i used to get mine running

[audijunky]

That is where myu cofussion comes in petejw. I runs good when its cold not great but good. Whwen it gets hot it runs like poopoo. So i am thinking rich. But when I had the sync done the plugs showed relly lean(white tips) So we turned the mix screws out two turns and now its too rich when warm. That is what I was trying to figure out. Could two turns out cause such a dramatic change. I have since turned them in a 1/4 turn. So now I am sitting at 3 1/4 turns out.
TADracer I had my mix screws at stock turns out too before the sync and my plugs were white, thats why my friend turned them another two turns out.

[skids]

Mixture screws can make a difference up to say 3000 rpms, but if you are blackening plugs above that, your pilot screws are probably not the only culpret.

Originally posted by audijunky
I have since turned them in a 1/4 turn. So now I am sitting at 3 1/4 turns out.
TADracer I had my mix screws at stock turns out too before the sync and my plugs were white, thats why my friend turned them another two turns out.

[petejw]

hey audi,
matey if ur going to put mufflers on and replace
ur current set up, ull b changing the jetting yet again,

but if its running like crap and u dont mind mucking about with it 4 now b4 u put the mufflers on, read the above link i put up,

as Alan said, for the purpose of jetting treat each circuit as individual to each other.

U say it runs ok cold but crap when its hot,
with the open headers ull never get low and mid running
as if u had mufflers attached or the air box, as previosly discussed, but in saying that when the mains kick in it should b hauling arse.

take the bike out let it run for 5 min, take it up 2 6000 and above,
how does it run compared with doing the same at operating temperature, start from there. if it runs crap when its hot at that rpm drop the main jet down a size, stick to the main until ur happy with performance.

then do the same for the mid range, by adjusting the slides,

and then with the pilots at operating temp screw the pilots in til lighly seated, and then slowly screw them out to u get to the highest rpm.
if ur mates a mechanic he should b able to set the mixtures screws correctly, dont just screw them out 4 the sake of screwing them out, and dont set them at spec thinking that may b right also, u should b able 2 clearly hear the difference when moving the screws, if not drop the idle a little, and make sure u havent broken of the tips.

its a thing that may take days or even weeks to achieve,
but i find it easier than doing the plug chop thingy and cheaper.

just reread the start of the thread again, if its sputtering and backfiring that would indicate a lean mixture and if its doing it around 5000 it could be ur slides are on the lean side. do u have the carbs with the adj slides if so try lifting the needle a notch.


hope it makes sense
let us know how u go.

[audijunky]

Thanks for the advice pete
I am probably gonna hold off til I put some muffler(s) on. I checked my plugs last night 1 is good tan, 2 rich black, 3 rich black wet, 4 white and lean. So now that I realize that there is an obvious problem what would cause this? I know the sync is good cause I helped him do it with the MERC sticks. Maybe my floats arent ali set exactly at the same hieght? I know the needles are all set the same. I am pretty sure about the mix screw positions. I know my floats could be screwed because of a previous attempt I made to get them at 25 mm. When setting these is it 25mm from the gasket surface, or do you remove the gasket and go off the carb body?
Thanks again for all your help.
I should probably not even touch any thing till I get some mufflers huh?

[Ken Talbot]

2 and 3 are linked electrically, i.e. they are fired by the same coil, which is triggered by the same pick-up coil and wires. That's where I would begin looking.

[audijunky]

haven't dug into that yet, that is under the cover on the right side of the crank correct??
And I am assuming you are telling me to look there because they can work fine when cool, but intermittenly when running hot?

[Ken Talbot]

The pick-up coils and wires are under the cover on the left side. There's a decent tech article on this in the tech section that will show you what to look for.