VM26SS carb problems 1979 GS750 EN

[rustynissan]

I have a 1979 GS750EN. It doesn't seem to go above 65mph currently. I have tried balancing the carbs, adjusting the air screws and checking for air leaks. It still seems like it is burning way too much fuel and the acceleration is very poor.

Any ideas?

More details can be found in this thread.

[BassCliff]

Greetings and Salutations!!

Hi Mr. rustynissan,

Give you bike some lovin' and go through the maintenance lists in your "mege-welcome". Let's get started.

I just stopped by to welcome you to the forum in my own, special way.

If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", the Carb Rebuild Series, and the Stator Papers. Now let me roll out the welcome mat for you...

Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

[Big T]

I'm just guessing that you are the victim of the dreaded PO (previous owner) syndrome

I'm having a bit of trouble understanding the basis of your problem

1. Will the bike pull to redline in gears 1,2,3? (that should be over 60 mph)
2. Do you have the stock airbox?
3. How old are your points and condensors? Have you inspected and adjusted them?
4, Is your advancer working?
5, What do your spark plugs look like?

If your air filter or mufflers not clogged, then I would say your cam timing is off.

Even if you have air leaks and your mixture is lean, VM carbs should allow the motor to rev close to red line

Also, where are you in WA. There's members all over the state, one may be able to offer some direct advice

[rustynissan]

1. Will the bike pull to redline in gears 1,2,3? (that should be over 60 mph)
2. Do you have the stock airbox?
3. How old are your points and condensors? Have you inspected and adjusted them?
4, Is your advancer working?
5, What do your spark plugs look like?

1. Been a few weeks since I've ridden it. My guess is no. Let me get back to you.
2. Yes. Stock airbox.
3. I imagine the points and condensers are original. (Bike only has 8,800mi). I have not looked at them.
4. No idea if advancer is working.
5. I just replaced the spark plugs. The old ones were definitely carbon-fouled (at least).

I am new to motorcycle maintenance, but I figure things out quickly. I just need someone to point me in the right direction I suppose. Thank you all for your patience.

[rustynissan]

Also, I live near Hood River, OR.

[tom203]

Even though you referenced you previous thread, starting a new one gets confusing for those of us with limited mental resources!
So the bike is new to you- do you know its history? Anyways, the place to start is Basscliff's emporium- lots of practical info that will explain what needs to be checked and why.
Have you checked inside your airbox to make sure a family of field mice have not made it their home? Not being able to hit 65 ? does it stumble or just feel like its got nothin left?

[Big T]

1. Been a few weeks since I've ridden it. My guess is no. Let me get back to you.
2. Yes. Stock airbox.
3. I imagine the points and condensers are original. (Bike only has 8,800mi). I have not looked at them.
4. No idea if advancer is working.
5. I just replaced the spark plugs. The old ones were definitely carbon-fouled (at least).

I am new to motorcycle maintenance, but I figure things out quickly. I just need someone to point me in the right direction I suppose. Thank you all for your patience.

The bike may have low miles, but things still age. I'd start with:

1. Adjusting the valves
2, Checking the timing and advance
3, Proper carb cleaning and setting
4. New O rings in carbs and at Head

It may be as simple as bad condensors, they do age.

Read thru BassCliff's site, it will give you all the maintenence tips plus a service manual

[rustynissan]

I should mention that I have checked the valve clearances and they are fine. I never took the intake boots off (I will most likely replace the o-rings anyways) and when I replaced the carbs after cleaning them, the bike was able to go about 90 without too much effort. Something happened about 2-5 minutes after opening it up on the highway to ruin the performance.

I am browsing through all the helpful links on the BikeCliff site... So much helpful information!

[Big T]

Does you bike have points?

If so, that's where I'd look

[rustynissan]

UPDATE:

I have found a potential problem. The capacitance of my condensers read 0.202uF and 0.158uF (the FSM I have specifies 0.18uF). The one with the lower capacitance is for cylinders 2&3. When I pulled the plugs recently, those plugs were black and a little wet looking (not really black, almost brown-black?) and the other two plugs were fine. I have noticed that the engine is missing frequently while riding.

I have also performed the weather-stripping fix for the airbox covers and filter seal.

I have purchased a new set of condensers, and have adjusted the timing statically. I will repost when I have installed them and get a chance to ride.

[Big T]

A bad condensor will do exactly that which you describe

Start your bike up with the points cover off, turn out the lights (at night,of course)

Is there sparking at the points? Yes, = bad condensor, no spark at plugs

[rustynissan]

I did that outside yesterday. I did notice that the points for cylinders 2&3 were sparking a lot. The other one only sparks occasionally. Now I am really excited for these condensers to show up in the mail. Thanks for the good news!

[TheCafeKid]

Big T is right. On a recent trip we took with a bike just like yours, with even less miles on it, it crapped a set of points and or condensors with no warning. One minute the bike was firing on all four, the next, it spat on two then four intermitantly. Changing the points and condensors cured it, but to fix it permanently, buy a Dyna S ignition system and set it and forget it. Does away with the P&C system in favour of electronic ignition.. 125 bucks will get ya one..

[Big T]

I did that outside yesterday. I did notice that the points for cylinders 2&3 were sparking a lot. The other one only sparks occasionally. Now I am really excited for these condensers to show up in the mail. Thanks for the good news!

Good,

then come down and ride with us sometime - you missed the rally

[TheCafeKid]

One other addition that I forgot to mention. The 77-79 750s used TWO different P&C set ups, and two different types of coils. Kukosan Densi and Nippon Densi set ups. The are NOT interchangeable, and the condensors from one will not fit the plate of the other. In fact, as I so recently found out, using the entire ignition plate from one make with the coils of the OTHER make will burn up your condensors in oh....about 700 miles..