Rejetting question

[Guest]

I have a 1983 GS1100L. I moved from Utah which has a sea level of 4600ft to now North Carolina with a sea level of 770ft. Bike is jetted for 4600ft. It runs good here with no throttle issues. Its very responsive. I have noticed louder Knocking than ever, I'm guessing thats from running a little lean. I checked the plugs and they look normal. I stopped running the bike until I got some advise from this forum. Only thing that has been added to intake/exhaust is a mac 4 into 1.

Question: Should I rejet the carbs even if it is running as good as it is (besides knocking)? If I do rejet couldn't I just go back to factory mains? Do they need balanced after a rejet? All 4 carburetors were cleaned and balanced last year. I know the mac 4 into 1 will have some differences but hoping not much. Any help is appreciated.

By the way, If anyone knows of a mechanic in the Greensboro NC area that wants to help work on my bike I will gladly pay them. No shop around here wants to touch it. And I don't have a garage anymore to work on it. New apartment complex said no way. But wont they dont see wont hurt.

thank you to any replies.

[koolaid_kid]

Your CV carbs should not need rejetting, that is one of their benefits.
The knocking is timing-related. Either retard the timing by a couple of degrees, or move up one octane rating on the gasoline you are feeding it. Most likely you have a different mixture in the fuel you are using, which is causing the knock.

[jbthomp]

Did you rejet when you put the 4-1 exhaust on it? If not you should have. I definitely would not ride it if it's knocking. That is a good way to tear some stuff up in a hurry. Lean mixtures are very dangerous for your engine. You can burn a valve or a piston real fast. How do your pipes look? Are they nice and chrome or blue? If they are blue that is a sure sign of running way too hot and lean.

[jbthomp]

? If I do rejet couldn't I just go back to factory mains?

If its lean you need more fuel not less.

[bill761mac]

Thank you Koolaid, Being your a senor member I will lean more towards what your saying. Im running 93 octane always have. unless 93 is different here in NC than it is in Utah. Wouldn't surprise me. I am leaning torwards the timing, will retard the timing and go from there. So CV carbs don't need to be rejeted? That is awesome. Everyone I have talked to said it has to be rejet.
Once again GSresourses has saved me money.

[GSX1000E]

Raise your main jets by at least 2 steps. BTDT

[koolaid_kid]

Raise your main jets by at least 2 steps. BTDT

Since you are already running 93 octane, this may be the proper solution.
Personally, I believe it to be timing. Before spending the money on the jets, try retarding the timing. One or the other should solve the issue.

[blowerbike]

there is very little adjustment on the timing plate plus you have an electronic advance model.
you could always file the slots a little to get some more retard....
could be carbon build up boosting the compression....maybe?

[koolaid_kid]

blowerbike, have you heard of anyone needing to rejet CV carbs for elevation changes?

[Steve]

Since you are already running 93 octane, this may be the proper solution.

Since higher-octane "premium" fuel burns slower, you need to advance the timing several degrees to get it to complete its burn in time.
With stock timing and "premium" fuel, the mixture is not being completely burned, robbing you of power.
My suggestion here is to go with the factory-recommended "regular" fuel.


bill-mac, your bike came from the factory with 115 main jets. With your MAC header, you might need something in the range of 120-125.
My suggestion is to remove the carbs and see exactly what you actually have in there, then decide what you need to do.

.

[koolaid_kid]

Steve, the issue is knock, which is usually pre-ignition. What is your opinion on that?

[jbthomp]

Spark knock can be caused by running too lean. He never said if the carbs were rejetted following the exhaust upgrade. Which probably they were not. Too hot of a heat range on the spark plugs can cause that too. Im sure the knock is not new it is just getting worse and now he is noticing it. Which mayhem is soon to happen inside his engine.

[wymple]

blowerbike, have you heard of anyone needing to rejet CV carbs for elevation changes?

Nearly 4000 ft less elevation is a bunch. I think he may be on the lean side, CVs or not. Cheap and easy to jet up a bit & maybe save a motor. I would see what's in there, & follow jbthomp's advice.

[koolaid_kid]

A quick plug read is in order.
Bill, what color are your plugs?

[koolaid_kid]

I agree. Who ever installed the pipe should have gone up about 2 sizes on the mains, but that does not mean they actually did the work.
Bill, you really need to pull a main jet and see what size it is.