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Warm days = loss of power

  • Thread starter Thread starter peterpressure
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peterpressure

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Been riding my 78 GS750 for a few months now. Worth enough to be my daily commuter, that is, except for slightly warmer and humid days.

All week the bike rode great, I even had to ride it on a cold rainy day and it rode without a hitch, but today, a nice sunny warm humid day, The bike stalled so many times when I came to a light or stop sign or just cruising in 2nd gear it would lose power and stall out. I'll take it out later tonight and I bet it will ride fine and not stall, because it really only seems to do this on warm days.

Any idea?

Coils overheating?

Points need to be cleaned?

I already replaced all but one O-ring from carbs intake boots, (One screw was stripped on the boot). I know I know, I need to check my valve clearances this weekend...

Any ideas?

I keep going back and forth between the Coil Relay Mod and stock wiring because I swear this happened less on the stock wiring which got me thinking it was a coil overheating issue. Perhaps I could hook up a temp gauge to one coil and see how hot it gets this weekend...
 
First thing I do on any 30 year old bike is make sure all the maintenance is up to date. That includes: fresh carb o-rings, intake boot o-rings, clean points, clean plugs, air filter, valve adjustment, etc. Until all this stuff is done, you are just shooting in the dark and guessing on what needs to be done.

BTW, poor running when warm can be several things including rich mixture, poor compression, poor spark... see what I mean? Too many things to attack, better to start with a solid foundation and build from there.
 
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Probably the good ol petcock. When it dies pop the fuel cap. Maybe Its not venting.
 
Nessism said:
First thing I do on any 30 year old bike is make sure all the maintenance is up to date. That includes: fresh carb o-rings, intake boot o-rings, clean points, clean plugs, air filter, valve adjustment, etc. Until all this stuff is done, you are just shooting in the dark and guessing on what needs to be done.

BTW, poor running when warm can be several things including rich mixture, poor compression, poor spark... see what I mean? Too many things to attack, better to start with a solid foundation and build from there.
Click to expand...

Bike has fresh carb o-rings and intake boot o-rings (cept for one boot). Have not cleaned the points or plugs, but cleaned the air filter.

I just read this entire old thread, similar issues to mine, and the solution was the valve clearances. http://www.thegsresources.com/_forum/showthread.php?t=100217

I think that is next on my list...

I went to do a Valve clearance check last weekend, but my head was so dirty and I could not find any tie wraps big enough... This weekend!!
 
bonanzadave said:
Probably the good ol petcock. When it dies pop the fuel cap. Maybe Its not venting.
Click to expand...

A comment on this check: Listening for a hiss when the cap is popped may be inconclusive. If you do hear it, you know the cap isn't venting. If you don't hear it, you might have missed it. The cap on my 850 was easy to disassemble and check visually, so I would recommend that method of checking.

Having said that, I agree with Nessism. The baseline maintenance needs to be done before any real troubleshooting can begin.
 
Just had to share this:

So I stopped by my local Suzuki Dealer to make sure they'll have some shims for me when I figure out which ones I need. I explain my situation to the mechanic, his reply "Oh I wouldnt bother checking your Valve Clearance, its not gonan fix the problem your having" "Besides a 30 year old bike with 50k miles on it probably isnt worth checking anyways."

haha...

They did have shims for me though...

He says my problems sounds carb related and that Ethanol is eating up everyone floats these days... haha...

funny
 
peterpressure said:
Just had to share this:

So I stopped by my local Suzuki Dealer to make sure they'll have some shims for me when I figure out which ones I need. I explain my situation to the mechanic, his reply "Oh I wouldnt bother checking your Valve Clearance, its not gonan fix the problem your having" "Besides a 30 year old bike with 50k miles on it probably isnt worth checking anyways."
Click to expand...

Do NOT under any circumstances, let this idiot work on your bike.
Moron.
 
i run whatever gas I please, and i have never had any problems with my floats getting eaten up....
 
I have seen floats with some funny looking deposits on them. But NONE eaten up. This guy is a moron. For some reason, shops seem to enjoy keeping morons around. Maybe it attracts other morons who might believe the crap that the moron they hired to fix bikes tell them. Next time you see that guy tell him *I* said he's a moron.
 
Im a Moron :-? When I did the carbs on my sons CM400T I broke a float and went across the street to Honda. They actually had one and I wanted to finish the project so I bit the bullet. Ouch, I think it was $60. One float...$60 !

Anyway, It was still in good shape just broke. Ethanol gas wont eat carb parts but it is very unstable and will start to break down in just weeks. The needle valves were shellacked in solid.
 
That guy may not be so much of a moron.
Look at it this way-he may be trying to see if YOU are a moron and sell that "old POS" to him on the cheap!
Or, he'll put in the "alky proof" floats for you at a really good price.....

see what I'm getting at?

Either way, keep him far, far away from your bike. In fact, find someone else to do bidness with.
 
Definitely go over all the basic stuff.

But I recently had some problems where my bike would sputter a little bit at idle when it got hot. It got worse and it would die in heavy rush-hour stop-and-go traffic and it was hard to start, and even on a good ride it wouldn't idle quite smoothly. I swapped a cold spare coil in and the problem went away.

I might still get new Dyna coils though and never worry about it again.
 
p_s said:
Definitely go over all the basic stuff.

But I recently had some problems where my bike would sputter a little bit at idle when it got hot. It got worse and it would die in heavy rush-hour stop-and-go traffic and it was hard to start, and even on a good ride it wouldn't idle quite smoothly. I swapped a cold spare coil in and the problem went away.

I might still get new Dyna coils though and never worry about it again.
Click to expand...


This is part of my fear, that it is the Coils overheating, I have heard your story a few times and it sounds spot on with mine. I'll look for some cheap spare coils til I can afford a Dyna S. Thanks for the idea..
 
peterpressure said:
This is part of my fear, that it is the Coils overheating, I have heard your story a few times and it sounds spot on with mine. I'll look for some cheap spare coils til I can afford a Dyna S. Thanks for the idea..
Click to expand...
I ultimately want Dyna coils, because I think I'd get the same problem again on a hot day in traffic with another used old coil.

But still, if you have a spare, you can at least warm up the engine, wait for the problem, then swap in a cold coil (takes 1 minute if you don't mount it), see if it goes away--then at least you know and you won't waste more time and money looking for other causes.
 
p_s said:
I ultimately want Dyna coils, because I think I'd get the same problem again on a hot day in traffic with another used old coil.

But still, if you have a spare, you can at least warm up the engine, wait for the problem, then swap in a cold coil (takes 1 minute if you don't mount it), see if it goes away--then at least you know and you won't waste more time and money looking for other causes.
Click to expand...


I just took her out for a ride, now that the sun is down and no issues, rode like a champ. I need to measure the R on my coils because my other concern is perhaps the PO did not realize points need a 5 ohm coil and use a 3 ohm instead from a newer bike. Its a mut bike so I wouldnt be suprised.

Tomorrow I'll measure the valve clearance and coils!
 
Accel Coils, 4.5 Ohms
Noticed the PO already converted to a Dyna S ignition, haha...

I'll take some pictures...
 
p_s said:
I ultimately want Dyna coils, because I think I'd get the same problem again on a hot day in traffic with another used old coil.
Click to expand...

Only if it's another bad used old coil.
Most of them work fine.
 
Ok, So I went to take my 78 GS750 for a ride, and its pretty hot out, so I knew I was in for trouble. Few blocks from home, stalled and she WILL NOT start. Battery is dead, went and got my car and a jumper pack, still won't start. I am starting to think my starter is bad in hot weather. The starter is PRETTY hot, is this normal?

I was on the way to change out my Valve Shims, so very soon, I will have that done too, just need to start her and drive her to my friends garage to do the job!
 
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