Author Topic: Engine stalls on idle (Read 5283 times)

mgTagGD · « **on:** November 03, 2005, 02:00:22 PM »

My engine works only on throtle and on load, even on low RPM. But in higher RPM if i close the throtle it cuts the ignition (i have backfire so i guess it is not carburation problem). If i stay on the throtle it rocks till 13.000 RPM

am i going for new CDI?
I mesured the coils and i got this values compared to the manual

coil1 primary 10ohm , secondary 23Kohm
coil2 primary 4ohm , secondary 23Kohm

manual says primary 2.5-3.8 ohm, secondary 30-50Kohm
and also "Exact ohmic readings are not necessary , but , if the windings are in sound condition , their continuity will be noted with these approximate values.

Carburators are cleaned but not balanced (i had rust problems but i think i am ok from that now)

engine idles only on choke even warm

Any help please?
My ignition is 32900-10D40 is any way to test it whith a polymeter?

interfuse · « **Reply #1 on:** November 03, 2005, 02:10:39 PM »

Sounds like clogged pilot jets to me... I had to clean mine out with a small wire inorder to remove the debris.

mgTagGD · « **Reply #2 on:** November 03, 2005, 02:17:39 PM »

How deep do i have to desassemply the carbs to reach pilot jets?
If i remove the diaphragm,piston valve etc am i there?

I havent mesured the height

interfuse · « **Reply #3 on:** November 03, 2005, 02:28:46 PM »

To reach the pilot jets you have to remove the float bowls and the floats. The pilot jets are under the little rubber plugs, deep in the carb body. I had to remove my carbs a couple of times to get all the pilots clean.

NCBANDIT · « **Reply #4 on:** November 03, 2005, 02:29:29 PM »

Remove bowls, you will see them.

I am assuming they are like most carbs.

mgTagGD · « **Reply #5 on:** November 04, 2005, 09:54:38 AM »

I found it but i had to unscrew it. Is this but? is it the same with the pilot screw that is preset? i have the manual but the pics are not very helpfull.
i dont know if this wos the pilot screw also.

I puted the carbs up , but it didnt run. I dint try much.
I will try again later

interfuse · « **Reply #6 on:** November 04, 2005, 11:04:04 AM »

I have a feeling you're not looking at the right thing. If your bike was running okay before, but just having problems idling LEAVE the fuel screws alone! If I can find a picture of the guts of a carb I'll point out were the pilot jets are but I wouldn't have time to do that until tonight.

interfuse · « **Reply #7 on:** November 04, 2005, 03:56:57 PM »

This picture is from a GS500. The GS carb bodies are the same as the gsf400 carbs. The area highlighted in pink is where the pilot jets are located. Deep inside. You can remove them with a flat head screw driver, but be careful because they are brass and strip easily.

Here are some other helpful links about cleaning Mikuni BST-33 carbs (different bikes, same carb body):

http://faq.f650.com/FAQs/CarbMiscFAQ.htm

http://gstwin.com/carb_work.htm

Herr Tod · « **Reply #8 on:** November 04, 2005, 07:33:27 PM »

Just a little notice about the pilot screws... turn these only a quarter in any direction and it totally changes the way the engine picks up. 33 mm carbs on 100 cc. A GS 500 has 33 mm carbs on 250 cc. The B4 has very weak pulses to the carb so these are very sensitive. A 125 cc two-stroke usually has a 28 mm carb. The B4 is actually ridiculous and a pain if you want your carbs to be 100%. I am even thinking of using smaller carbs with more flow than the stock 33 mm's, as this would boost mid and peak power with less fuel consumption.

stripes1976 · « **Reply #9 on:** November 04, 2005, 10:28:32 PM »

you wanna try a gsxr400 gk76a sp model they have a 35mm per 100cc

gsxr400 racer · « **Reply #10 on:** November 05, 2005, 02:09:58 AM »

Quote from: "Herr Tod"

. I am even thinking of using smaller carbs with more flow than the stock 33 mm's, as this would boost mid and peak power with less fuel consumption.

wouldnt help peak power at all just midrange but if ya want smaller ones someone on the board would by your 33 's off ya real quick im sure!

Herr Tod · « **Reply #11 on:** November 05, 2005, 10:12:23 AM »

If they flow more than a stock 33 it does help peak power. Because they are smaller than a 33 they react better to the engine pulses and that helps mid power

gsxr400 racer · « **Reply #12 on:** November 05, 2005, 10:55:31 AM »

Bigger carbs more top end but lose bottum end some, Keep in mind the GK76 gsxr 400 SP has 35mm carbs and the same basic engine!

gsxr400 racer · « **Reply #13 on:** November 05, 2005, 10:58:26 AM »

A 125 cc two-stroke usually has a 28 mm carb

And a 2 stoke is tottal different you cant compare apples to oranges!

Herr Tod · « **Reply #14 on:** November 05, 2005, 01:05:38 PM »

It's more like two different kinds of apples. They can both have the same carbs, they both flow air. Only difference is the quantity of air per rotation and a few other variables which are not really important in this case.

It's all got to do with the amount of airflow (cc's per minute). Some manufacturers name their carbs after the amount of air they can flow instead of the diameter. Same goes for jets, I can have ten #100 jets, all with a different hole size but with the same flow. Carb manufacturers name the jets by using a flowbench to test each one.

The carbs adresses it's various systems (slow, main, etc.) according to the engine's pulses. Naturally a '100cc' pulse in a small venturi is more powerful than the same pulse in a very large venturi. Hence the B4 is very sensative to carb changes. If the carbs were smaller but with the same airflow, top end will stay the same but the lower end will be improved because the carb can adress it's systems better and faster.