GS1000 running rough...help!!!

[Anonymous]

After spending much time and effort getting my GS1000 into a roadworthy state, I've found that there is still one problem remaining.
It starts and idles perfectly (carbs and ignition overhauled to overcome lots of problems...carbs full of gunge, points and wiring, etc.). It revs to at least 6500-7000rpm in every gear after I've ridden it for 4 or 5 miles to warm it up, but once I've done 10 or 12 miles it starts to misfire over 4500rpm and just won't pull beyond this. So basically it runs worse when up to full working temperature.
What's going on? What should I check...fuel level, electrical gremlin,???

Thanks
Yoshi

 

[Anonymous]

I would start by insuring the choke is opening completely.

Tim

 

[saaz]

What model GS is it? Electronic ignition, CV carbs etc? I would suspect a mixture problem (too lean once warmed up). A lean conditon should not make it misfire if it has been running ok before warming up - more a surging. Try running it at the playing up temp for a little while, then turn it off and check the spark plugs. I have had wiskers of carbon on the plugs resulting in a similar condition. If it is to lean the plugs will look very white and signs of melting the electrodes.

Otherwise could be a CV carb problem, electronic problem that results when warm etc etc.

 

[SqDancerLynn1]

I would suspect the the fuel is contaminated with rust fron the tank and cloging the carb jets. I went thru something similer with my GS850. Drain the float bowls into a container and see what comes out. if there is any indication of rust there is your problem

 

[Anonymous]

If it helps, its a 1978 GS1000HC with later 'big-port' head and CV carbs. I wouldn't describe it as a 'surging' but what do I know!?! I might try plug-chopping it while its running in the misfire zone - this might tell me more. The carbs have been cleaned thoroughly, and I'm running a fuel filter just to make sure...but I guess I might have to look in there again!

 

[saaz]

Fuel blockages are possible. Check to make sure the fuel filter is not clogged and fuel is flowing out of the tap. Usually the problemn with CV carbs is lean running while cold and ok while warm.....

 

[Anonymous]

I'd be more inclined to look on the electrical side, coil insulation breaking down when coil gets hot, that kind of thing.

 

[Jay B]

How much junk is in the tank. It could be that after warming up the junk in the tank is beginning to block the internal screen. This will stop when the bike is shut off and set for a few minutes. May be time to clean the tank. One way to check it is to switch from on to prime of reserve. If it clears than that might be the problem

 

[earlfor]

Re: GS1000 running rough...help!!!

Hmmmm, my GS750 in 1st or 2nd gear will peg the tach. It seems to me that if you can only get 6500 rpm or so at best even in the lower gears, something is not quite right. Have you checking ignition timing with a timing light or was it static timed?

That it starts and idles perfectly suggests to me that the carb rebuild work you did is most likely pretty decent as usually being less than thorough results in poor idle and starting.

I think a major clue is that the problem gets worse when the engine warms up. I dont think engine heat is the direct cause, but rather, the question becomes: What can change due to running time? Most probable answer,..... electrical resistances. I think most likely is a coil breaking down or faulty plug caps, bad coil ground, or bad wiring connectors. I would try taking the bike for a ride and when it get to the point where it is missing at 4500 rpm or so, I would find the worst rpm range and ride it for a couple miles in this range. Then stop, and pull the plugs and look at them to see which ones are not running as they should. I.E. wet?, sooty, oily, etc.? That you are able to maintain 4500 rpm suggests that the problem is not on all four cylinders. If it is on two cylinders (for example 1 and 4) then that indicates a single coil. If the problem were to be on cylinders 1 and 3, then it is not a coil problem as one coil fires 1 and 4 and the other fires 2 and 3. If it is a coil problem, you will have a matched pair of cylinders that are the problem. A single cylinder could be nothing more than a faulty spark plug boot resistor. Bad grounds will cause the problem on all four cylinders or matched pairs, but not on single cylinders.

Usually, the most common problems are electrical related rather than mechanical.

Earl

After spending much time and effort getting my GS1000 into a roadworthy state, I've found that t
here is still one problem remaining.
It starts and idles perfectly (carbs and ignition overhauled to overcome lots of problems...carbs full of gunge, points and wiring, etc.). It revs to at least 6500-7000rpm in every gear after I've ridden it for 4 or 5 miles to warm it up, but once I've done 10 or 12 miles it starts to misfire over 4500rpm and just won't pull beyond this. So basically it runs worse when up to full working temperature.
What's going on? What should I check...fuel level, electrical gremlin,???

Thanks
Yoshi

 

[Anonymous]

The tank and fuel tap had been cleaned, and the tap flows correctly in all positions - I did try switching to prime but it made no difference.
I am (usually) mechanically sympathetic and don't like redlining the GS until its fully warmed up, so the 6.5-7k rpm was just an example. I'm sure it would rev further when cold, but I don't like doing it!
Hot or cold tick-over is nice and steady - I set it to about 1250rpm, although its fine down to 1000rpm.
I'm going to take it out in the next couple of days and try again - take it into the misfire zone for a minute or so, and then pull the plugs. It'll be interesting to see if its a pair of cylinders or all 4?!?
I'll keep you posted about what I find, but if anyone has any more suggestions I'd be pleased to hear them.
Just an afterthought, but what would happen if the primary wires to the coils were reversed or switched? I guess I'm asking if the coils have polarity?

Thanks all
Yoshi

 

[Anonymous]

The ignition coil for cyls. 2 and 3 is held on by one bolt (and a cable tie) as the front mounting on the frame has been broken at some point...am I correct in thinking that this is used to earth the coil??? Anyway, I ran a short wire between the front mounts of the 2 coils, and it seems to run better. I did about 30 miles on it today (77 degree ambient temp.) and it was running easily to 6000rpm/100mph. Taking it to 6500rpm/110mph was the limit as the misfire set in again, but it looks as if I am working in the right direction. I will only be happy when I get 8500rpm and 140mph! Any tips or advice to help with further improvements would be appreciated (...again!!!)

Thanks
Yoshi

 

[earlfor]

Considering that adding a ground resulted in a major improvement in performance, I would check the rest of the ignition system related contacts, both grounds and positive leads. After that, I would put a timing light on it and make sure the ignition timing is set correctly.

Earl

Anyway, I ran a short wire between the front mounts of the 2 coils, and it seems to run better.

 

[Anonymous]

Thanks for replying so quickly...I'll soon have memorized the colour, position and function of every wire in the GS loom!!! I'll let you know what happens.

Thanks again
Yoshi

 

[Anonymous]

Condensators???!!!!
If the ignitions is stock you have point-brakers and condensators.
I had the same problem on my GS1000 -78. Then I had done everything else I replaced the condensators and the bike runs like a new one.

Lars

 

[Don Lobacz]

You say big port heads with CV carbs? What air filters are you running? have you changed jets from stock? What main jets are in there now? I ask this because you probably don't have the stock airbox on there with the switch to CVs.

 

[Jay B]

Have you got air comming in one of the fuel lines or in the intake boots. Could be causing it to miss at certain RPMs as well. Use the carb cleaner trick to find out.

 

[Anonymous]

Have I discovered the problem?!?!?!? (long post)

Have I discovered the problem?!?!?!? (long post)

Checked all of the wiring again, and then double checked it to make sure. I added a couple of extra earths to make triple sure! Checked for air leaks round the intakes, none found. I'd previously cleaned the carbs and fuel tap thoroughly being careful to set the float heights correctly and check jet sizes. Points were replaced a while back and ignition timing is still fine. Coils, leads and boots were swapped with a (good) set from another GS1000.
It starts first push of the button, ticks over as well as any GS, and runs cleanly to 6500-7000rpm and then doesn't want to go any further. I felt that I had checked everything, so started thinking what there could be that I hadn't checked...well, when I cleaned the carbs and tap, and flushed out the tank I took the often given advice and put a (motorcycle) fuel filter inline between tap and carbs. :idea: It occurred to me today that maybe it is restricting flow, so I tried a brief experiment and measured fuel flow rate with and without filter. I used a brand new filter of the same type I had used before, and found it took about 60 seconds to flow 1 pint. Without the filter it took 30 seconds! This was with the tap set to Prime, but I guess the result would be the same in the On and Reserve positions. The filter reduces flow by 50%!!! 8O This type of filter had been recommended to me by more than one parts supplier, so I'm not very happy. But, have I found the problem?...when the rain clears, I'll found out and let you all know.

Regards
Yoshi

 

[saaz]

Sounds a bit like fuel starvation. It is a bit more difficult these days to find a fuel filter that works under gravity, not fuel pump pressure.

 

[Anonymous]

Running without the fuel filter makes absolutely no difference...oh dear, more head scratching to follow...

Yoshi

 

[Anonymous]

I'm now wondering how good those 'good' replacement coils, leads and plug caps are?!? New plug caps next then...