Finding the ideal idle mixture

[Vickersguy]

I don't have access to an exhaust gas analyzer which would easily solve this. I have a steady even idle at a normal speed. I have the pilot jet screws set at 2 1/2 turns out. Earlier I had them set at 1 1/2 turns and the idle was weak and the pipes quickly turned blue after a 1/2 mile test drive. I believe that was way too lean. Things seem OK now, but the color tune has a way too wide window for the "blue" condition, basically from 1 1/2 turn to 3 1/2 turns on the pilot screw. I will chase better mileage later with the needle kit from skydoc, and by reading the plug colors, but for right now I am looking at having a more accurate idle mixture. The basic have been covered. I have a hot spark on all cylinders, good compression, and the carbs are totally clean and synced. Perhaps I'm picking nits here. If so, let me know.

The symptom I'm concerned about is that my venture requires several minutes from the initial start, before I can ride off on it. Once it's warmed up enough to shut off the enriching circuit to about 1/2 choke, I'm good and the engine is strong enough to ride. After 2 minutes of riding, the enrichener can be shut off completely. Prior to that, it stalls easily. So it seems clear that I'm probably still a little lean. I was speculating that the final adjustments might be done with an IR lazer thermometer.

The parameters of of the process of getting useful data from an IR reading are daunting. A patch of flat black paint is needed so the reflectivity is the same on all pipes. There is the problem of the forward cylinders having a double wall and the rear cylinders having a single wall. Lastly, what temperatures am I looking for ? There are many other variables, how long and how hard the engine was run prior to the measurements, how long it sat at idle before measurements, ambient temperatures when the measurements are taken and so forth. The IR themometer is good if you have a cylinder that is not firing and spots that easily but can it be used for anything beyond gross adjustments ? Has anyone done this ? If so, what did you do ?

[Marcarl]

I'm kind of oldschool on this and mostly not all that concerned about things being dead on. They need to be close but I don't get myself all in a snit because, or just because.

So to do a review, again in my humble opinion, the bike has a carb, and not a computer fuel injected system, so something needs to be adjusted to account for a cold engine, because we all know that a warm engine uses fuel much more effectively than a cold engine. So there is a possibility of a choke or in this case an enrichment circuit. It's there for a reason and the reason being that the engine is much easier to start and runs better on a cold start with a richer fuel mixture. When the engine gets hot, then whatever the carbs are set for will do a fine job, but the engine needs to be hot, and that doesn't happen in 2 minutes necessarily. Some others claim to be able to start their bikes just fine with no enrichment, and that to me says that the idle circuit is too rich. The system is designed with a cold start enrichment system so no harm in using it. When I took the riders training course, the instructions were: start your bike, put on your gear and only then is your bike ready to ride, it takes a couple of minutes to put on your gear I found out.

Now on how I set the idle mixture: I hook a single vacuum gauge to all 4 intakes through manifold. I will first balance all the carbs (sync), then I will adjust the idle mixture to highest vacuum on each carb, then re-balance the carbs and then again adjust the idle vacuum for each carb. If an idle mixture screw doesn't have a response on the vacuum gauge, then the circuit is plugged and needs to be cleaned.

[MiCarl]

Lean runs hot so unless there is some sort of reference out there the IR thermometer won't help you.

 

I like to use a digital tach. Turn each cylinder to the fastest idle speed then make it richer until the RPM starts to fall off. You have to reset the idle to 1000RPM after each cylinder because setting them up at a different speed will have them incorrect for 1000RPM.

[tz89]

Now on how I set the idle mixture: I hook a single vacuum gauge to all 4 intakes through manifold. I will first balance all the carbs (sync), then I will adjust the idle mixture to highest vacuum on each carb, then re-balance the carbs and then again adjust the idle vacuum for each carb. If an idle mixture screw doesn't have a response on the vacuum gauge, then the circuit is plugged and needs to be cleaned.

 

I think you are saying that you adjust the idle mixture for best performance using a vacuum measurement as a proxy for performance. I don't think you are saying that a vacuum gauge can in effect detect a blockage in the enrichment circuit - only that an enrichment circuit that is blocked or badly adjusted has an effect on performance.

[Marcarl]

I think you are saying that you adjust the idle mixture for best performance using a vacuum measurement as a proxy for performance. I don't think you are saying that a vacuum gauge can in effect detect a blockage in the enrichment circuit - only that an enrichment circuit that is blocked or badly adjusted has an effect on performance.

The enrichment valve and the idle circuit are two different items. Yes you're right, the vacuum measurement is for best performance and should be done with a fully warmed up engine, and if there would be a choke, then the choke would have to be fully open. But seeing as there is no choke on these machines, it only needs to be fully warm with the idle enrichment off so that it runs, as best it will, in proper running mode, or default if you will. This setup only checks the idle circuit, the enrichment valve is a whole different ball game.

[Du-Rron]

I don't have access to an exhaust gas analyzer which would easily solve this. ..

 

I don't know anything about 1st gen Ventures. But, on a lean drop idle, if you can't get it, you have to replace, yes replace, the pilot screws cause something is wrong with them. And, maybe... the pilot jets are not as clean as you may think either. Here is a lean drop from another bike as an example. ignore the 3 3/8 turns out to start if that won't work for you.

 

 

The above is for a pilot screw that adjusts for AIR. You will need to screw IN to adjust for GAS like in the Venture

Edited March 25, 2019 by Du-Rron

[RDawson]

I'm definitely not great with carbs. This is the one thing I hope to address on mine at MD with some help.

[Vickersguy]

This was not a well thought out question on my part.. I've considered this for a bit and I don't think there is any way to use an IR thermometer as a substitute for an exhaust gas analyzer. While an IR meter is awesome for troubleshooting cylinder that is not firing or firing intermittently, it's not useful for tuning. The processes suggested by the folks who've replied here are better alternatives than fussing with a tool never designed for that task. Thanks to all of you that weighed in on this.

[Patch]

I don't know anything about 1st gen Ventures. But, on a lean drop idle, if you can't get it, you have to replace, yes replace, the pilot screws cause something is wrong with them. And, maybe... the pilot jets are not as clean as you may think either. Here is a lean drop from another bike as an example. ignore the 3 3/8 turns out to start if that won't work for you.

 

https://www.venturerider.org/forum/attachment.php?attachmentid=115860

 

The above is for a pilot screw that adjusts for AIR. You will need to screw IN to adjust for GAS like in the Venture

 

OH YAH BRO!

 

So first thing is atop for a moment and think thru what and why you feel somethin is up!

 

PILOT... at 3.5 turns you are semi restricted, meaning they leak okish but...... That may change with a couple of hard rides and some conditioner???????

 

1 3/4 is give or take ok, because ,,it is only the pilot we are discussing 2 1/2 is also okish or at least of little concern.

 

YOU MUST FIRST READ COMPRESSION, then troubleshoot, or just think she's all in caus you don't know different.

Patch