RPMs increase and decrease with blinker?

[Kentman7]

Hello.

I have a 1983 Suzuki GS300L.

the carbs have been cleaned and rebuilt, float valves adjusted, valve clearance done, timing done, and has no air leaks.

the bike is idling great at the moment, but will not react to the throttle. The RPMs refuse to increase with the throttle.

now to the weird part… as the bike is idling, I engage the blinker system and the bike starts revving up and down with the blinker signal. Blinker flashes on… RPMs increase…. Blinker flashes off… RPMs decrease.

any ideas what could be going on ?

thanks, Kent.

 

[650Skull]

Have you tried to operate the carb, (when running/idling), by hand at the throttle linkage.

 

[Kentman7]

I have not tried that. But I can see that the throttle cable is working and manipulating the main carb valves. And when I took the carb out, the main carb valves were working just fine by hand. I did inspect them when they were out.

it seems to me that I have two issues going on, a carb issue and an electrical issue.

the carb issue I think is gas starvation, that’s why I re- adjusted the float valves. It’s not getting enough fuel for the main jet when throttling.

I just had the carbs off and everything looked great. Diaphragms we’re working and look good, main jets/ air jets/ pilot jets were not clogged.

im thinking the problem is either the petcok or fuel filter at this point. Maybe the fuel filter is not letting enough fuel down the pipe when the main jets turn in and need more fuel? Or the petcok is partialy blocked? The bike has no problem idling.

as far as electrical goes, I have no flippin idea.

 

[gsme]

Check your grounds, make sure all ground connections (engine, signals, all)are clean and tight. Bad grounds will cause strange electrical issues.

As far as the running.I had a Honda CB400t that would not take throttle but idle fine. Try raising the needles in the throttle valves a bit, after ensuring that your fuel flow is good. Also make sure your intakes are not sucking air, check the o rings.

 

[Burque73]

I'll take a stab at the fuel issue.

Have you ran the engine with an auxiliary fuel tank? If you've just been using the bike's tank, have you always had the cap on? The tiny vent hole in the cap may be plugged.

 

[Kentman7]

I'll take a stab at the fuel issue.

Have you ran the engine with an auxiliary fuel tank? If you've just been using the bike's tank, have you always had the cap on? The tiny vent hole in the cap may be plugged.

I have run the engine with an auxiliary tank, but I can’t remember if I was having the throttle issue.

but the cap has always been on the tank when I have been running it. I will check the vent hole. But would you think if that hole is clogged, the idle would suffer as well?

 

[Kentman7]

Check your grounds, make sure all ground connections (engine, signals, all)are clean and tight. Bad grounds will cause strange electrical issues.

As far as the running.I had a Honda CB400t that would not take throttle but idle fine. Try raising the needles in the throttle valves a bit, after ensuring that your fuel flow is good. Also make sure your intakes are not sucking air, check the o rings.

To test the intake, could I spray some brake clean while it’s idling ? If there is a changed in RPMs, there must be a leak?

 

[Burque73]

I have run the engine with an auxiliary tank, but I can’t remember if I was having the throttle issue.

but the cap has always been on the tank when I have been running it. I will check the vent hole. But would you think if that hole is clogged, the idle would suffer as well?

Maybe if your tank was completely full, but probably not the issue, honestly. If the vent is clogged it creates a vacuum in the tank and fuel won't come out (as quickly). To check if that's the problem simply remove the cap and start it.

Also, have you downloaded a wiring diagram and followed the blinker wire to see if it passes through the same spot as an ignition wire, or power to the coils? As mentioned above, mybe they share a ground somewhere and it's corroded?

Just throwing this stuff out there.

 

[Kentman7]

Maybe if your tank was completely full, but probably not the issue, honestly. If the vent is clogged it creates a vacuum in the tank and fuel won't come out (as quickly). To check if that's the problem simply remove the cap and start it.

Also, have you downloaded a wiring diagram and followed the blinker wire to see if it passes through the same spot as an ignition wire, or power to the coils? As mentioned above, mybe they share a ground somewhere and it's corroded?

Just throwing this stuff out there.

I just checked the fuel tank cap, nothing plugged up.

I have also checked all the wiring, and it is all in good shape. Everything looks tight, snug, nothing out of the ordinary… that a very amateur mechanic can see…

this bike only has1400 original miles on it. It sat for the majority of its life. But whoever stored it, stored it right. It is in great shape!

I sprayed brake clean around areas that could have an air leak and found nothing.

the RPMs also increase when I apply the brakes. It will rev up like I’m turning the throttle.

is the vacuum inlet screw on theses bikes specially for balancing the carbs ?

 

[rphillips]

This really has my interest, something really off... Be sure you didn't, by mistake, hook the brake light wire to the carb., and the throttle cable to the brake light.... Trying to imagine how anything electrical, on these old bikes, could affect the fuel flow. Also can't imagine spark to "raise" the rpm.... I dun'no !!

 

[Kentman7]

This really has my interest, something really off... Be sure you didn't, by mistake, hook the brake light wire to the carb., and the throttle cable to the brake light.... Trying to imagine how anything electrical, on these old bikes, could affect the fuel flow. Also can't imagine spark to "raise" the rpm.... I dun'no !!

I have 2 connections on each the positive and the negative terminals to the battery. One of them is definitely the starter system.

I don’t know what the other connection is, probably the blinker/ lights/ horn etc.

it is so strange. The bike idles perfectly.

Maybe I have a weird electric connection AND enough gas going through the pilot idle system that is creating the RPMs to increase? I have know idea.

 

[pdqford]

Let's try to see if the electrical system is causing the issue..

Put your volt meter across the battery terminals.
What is the voltage

Start and idle the engine.
What is the battery voltage?

Activate the brake light
What is the battery voltage with the brake light on?

Release the brake light.

Take the positive lead of your volt meter off the positive battery terminal and put it on the positive side of the ignition coil
What is the voltage at the positive side of the ignition coil?

Activate the brake light.
What is the voltage available at the ignition coil.?


Oh! Just for the heck of it, will the engine rev up with the brake light on??

 

[Cipher]

This really has my interest, something really off... Be sure you didn't, by mistake, hook the brake light wire to the carb., and the throttle cable to the brake light.... Trying to imagine how anything electrical, on these old bikes, could affect the fuel flow. Also can't imagine spark to "raise" the rpm.... I dun'no !!

Its likely some sort of grounding issue.

 

[Kentman7]

Let's try to see if the electrical system is causing the issue..

Put your volt meter across the battery terminals.
What is the voltage

Start and idle the engine.
What is the battery voltage?

Activate the brake light
What is the battery voltage with the brake light on?

Release the brake light.

Take the positive lead of your volt meter off the positive battery terminal and put it on the positive side of the ignition coil
What is the voltage at the positive side of the ignition coil?

Activate the brake light.
What is the voltage available at the ignition coil.?


Oh! Just for the heck of it, will the engine rev up with the brake light on??

Will do. Thank you for the tips.

and yes, the engine will rev up when I engage either the front or rear brakes.

 

[Kentman7]

As far as the carburetor issue goes, which I think I also have a carburetor problem, because the bike will not throttle up whatsoever when I engage the throttle.

The carburetor has been cleaned and rebuilt, and all the jets and airways have been tested with carb cleaner blowouts. Needle jet diaphragms are going up and down nicely.
Idle and choke are both working well. I have new gas going through an inline filter. I tested for air leaks with some break cleaner. Petcok and float valves are working and flowing, hence a great idle for extend amount of time.

The only issue that I can see right now with the carb is that it does not have a pilot jet “plug”. There is even a housing for this pilot jet plug on my carburetor. A plug would fit right in it. It looks like it is designed for a plug. BUT, the parts specs for the GS300L doesn’t have any mention of a plug, even though the GS450 had them. Other than that everything is working fine!

I don’t know if the electrical issue is messing with the carb throttle up. I wouldn't think it would. The carb has no electrical hook up to it. It’s a different system, right?

Do you think this bike has an electrical connection that goes from the throttle to the ignition system? Something that tells the bike to increase the spark? I did not see any in the service manual.

 

[Cipher]

As far as the carburetor issue goes, which I think I also have a carburetor problem, because the bike will not throttle up whatsoever when I engage the throttle.

The carburetor has been cleaned and rebuilt, and all the jets and airways have been tested with carb cleaner blowouts. Needle jet diaphragms are going up and down nicely.
Idle and choke are both working well. I have new gas going through an inline filter. I tested for air leaks with some break cleaner. Petcok and float valves are working and flowing, hence a great idle for extend amount of time.

The only issue that I can see right now with the carb is that it does not have a pilot jet “plug”. There is even a housing for this pilot jet plug on my carburetor. A plug would fit right in it. It looks like it is designed for a plug. BUT, the parts specs for the GS300L doesn’t have any mention of a plug, even though the GS450 had them. Other than that everything is working fine!

I don’t know if the electrical issue is messing with the carb throttle up. I wouldn't think it would. The carb has no electrical hook up to it. It’s a different system, right?

Do you think this bike has an electrical connection that goes from the throttle to the ignition system? Something that tells the bike to increase the spark? I did not see any in the service manual.

clean the grounds and put on the pipes and airbox\filter

 

[rphillips]

Very interesting, just can't imagine anything electrical making the revs go "up" on these old bikes. Wondering how much the revs rise when brake light comes on.

 

[pdqford]

and yes, the engine will rev up when I engage either the front or rear brakes.

Sorry, that’s not what I was trying to get at.
To use your terminology, I should have asked if the engine will “throttle up” when the brake light is on?

(Thinking you may have a marginal shared ground that is reducing current to the coils, but the ground improves with more current (i.e., brake light current) added to the ground. Any loose or cruddy grounds? Do you have the wiring diagram?)

 

[rphillips]

No doubt grounding problems can cause all kinds of strange things to happen. but changes to the coil ground or brale light making the rpm rise or throttle response better, I'm missing it.

 

[pdqford]

I am grabbing at straws, but thinking if the brake light sends more current through the shared ground, that may improve the current through the coils.
That’s why I am curious to see what the coil voltage is before and after the brake light comes on.