GS1100E performance

[rasndas]

Sorry if this has been covered before but I couldn't find a thread using the searh function. I have a stock 1983 GS1100E with the exception of a old vance and hines 4 into 1 exhaust. The motor has 50,000 miles on it and seems to run great but I am wondering about the top end performance. It accelerates very hard to about 100 MPH but then seems to run out of steam. I have had it to 115 but at that speed it is about done ( very little acceleration). The jetting is stock but the plugs look great ( very light tan). The advancer is working and the timing is set per the owners manual. Valves are adjusted. Compression is 100-105 psig in all 4 cylinders ( on the low side but still in servicable limit). Does this sound reasonable for a stock bike? I also have a GS700ES with a Yosh pipe and PODS ( Carbs have been rejettet for this) it does not accelerate as hard as the 1100 but has a higher top end speed so I was just wondering.

 

[Nessism]

It might be lean on the main jet. Some plug chops might be in order. Your tan plugs may be a result of the low speed jetting being okay (where the engine spends most of it's time), but it could still be lean on the main.

 

[rasndas]

I had slightly richer main jets in it and it would miss at full throttle higher RPM. I should add those jets appeared to be dyna jet jets and were number 115 ( I think ). Going back to the factory main jets allowed it to run cleanly. The bike does have the stock airbox in place.

 

[Nicholaschase29]

dynojets aren't the same as mikuni.

http://www.vmaxoutlaw.com/tech/dyno-mikuni.htm

 

[hampshirehog]

According to this: http://www.jockeyjournal.com/forum/showthread.php?t=64769 your 115 Dynojet mains were the same as the 107.5 Mikuni mains your bike runs as standard.

Is everything else in your carbs stock and is the air filter clean?

Don't forget to check your fuel tap - at 115mph and WOT your carbs will be drinking petrol like it's going out of fashion and the tap / filter will have to be flowing A1 to cope with the demand.

 

[posplayr]

According to this: http://www.jockeyjournal.com/forum/showthread.php?t=64769 your 115 Dynojet mains were the same as the 107.5 Mikuni mains your bike runs as standard.

Is everything else in your carbs stock and is the air filter clean?

Don't forget to check your fuel tap - at 115mph and WOT your carbs will be drinking petrol like it's going out of fashion and the tap / filter will have to be flowing A1 to cope with the demand.

With the 4:1 he is probably running lean and needs to increase the jetting. With pods and the 4:1 he should be at DJ 132-138

 

[rasndas]

The jets per my shop manual are 112.5 ( which is what I installed) and ran leaner than the dynojets. At least the missing stopped. A plug chop with new plugs is probably in order. The ones that looked good had a couple of thousand miles on them. It is not like I run the bike that hard very often and finding a place to run it that hard for any distance is not that easy either. Never considered the petcock. It doesn't miss or have any type of hesitation just kind of runs out of steam at that speed. What kind of top end do you guys with a stock bike see and how fast does it get there?

 

[hampshirehog]

Those main jet figs I used were for the earlier 1100 - your 112.5s are right for your year - my mistake for not reading your post properly. But this means that the Dynojet mains you removed were smaller than the Mikuni jets you replaced them with. And yet it ran leaner - odd?

115mph on a stock 1100 is easy - you can get there in the blink of an eye accelerating hard (and then back off as you realise you're going so fast). You've got something wrong somewhere - either that or your 40 stones and towing a parachute. I guess your chain and sprockets aren't shagged and the brakes aren't binding?

Plug chops would be my first port of call - low speed in top, a long hill and WOT for a short burst will show you what's happening.

 

[Nicholaschase29]

with smoothbores and a 4-1 and some other things I was over 140 (on the speedo) I have the reverse problem with my 700... I only get to about 115 and it's done. pods and pipe. messed with it forever - never nailed that one.

 

[Guest]

Throw some 117.5 main jets in it and go
Those compression numbers are on a warm engine with the throttle wide open?
I wouldn't think top speed would be much more than 125mph with a stock motor.
My 1230 was at 135 with a barn door.

 

[trippivot]

what RPM are you at in top gear when it slows? does it do the same thing in 4th gear at the same RPM?

the final gearing, is it stock too? a 630-14 sprocket up front will have you topped out at 110 no matter what jetting you have.

have you tried the enrichner/choke when it is W.O.T. and at the end of it's accelleration? to enrichen the engine as a diagnostic

 

[Roger P.]

Pulling out to pass a line of four cars from 100 km/h had me over 220 km/h by the time I pulled back in. I think you have a very sick 1100 there. And I know mine is running lean.

 

[jimb12]

With a VHR pipe and the airbox you should use around a 115 main jet (genuine Mikuni).
Your compression is very weak, as I recall my '82 EZ had around 150psi on the good cylinders when I checked it. Given such a large difference, it looks like yours needs to be freshened up.
That bike should run over 110mph in just a 1/4 mile dragstrip run (assuming the rider isn't huge).

 

[davel]

With a VHR pipe and the airbox you should use around a 115 main jet (genuine Mikuni).
Your compression is very weak, as I recall my '82 EZ had around 150psi on the good cylinders when I checked it. Given such a large difference, it looks like yours needs to be freshened up.
That bike should run over 110mph in just a 1/4 mile dragstrip run (assuming the rider isn't huge).

I agree with this. My 82 GS1100E with 40,000 miles has 150psi across all cyl. As mentioned earlier, make sure to take the readings with the engine warm and throttle wide open.

A good running stock GS1100E will have 90+ rwhp and top out round 135-140mph

 

[rasndas]

Thanks for all the input. Have not had a chance to do plug chops yet but will get to it as soon as weather and time permits. The compression tests were done on a warm motor but I neglecteted to open the throttle fully. My compression tester is one for a car which I built an adapter for to fit the bike. it has more volume in the hose and adapter than a unit deaigned for the bike alone and that would probably account for a somewhat lowere reading. Also the gage hasn't been calibrated so I can't vouch for its accuracy I was mainly looking for consistaincy between the cylinders which it has. The gearing is stock along with the rest of the bike ( Except for the header. Acceleartion is ferocious ( arm stretching scary I also have a 2001 ZRX 1200R kawasaki so I am familiar with fairly hard accelerationg bikes) up to 100MPH or so and then starts to flatten off. This really isn't a huge concern as 100MPH is very fast for me anyway. I will do the plug chops and get back with you guy's. Could the stock gearing be too short?

 

[headsbikesmopars]

I believe you have a high gear leanout. Poping and cracking (missing) is classic leanout symptoms. Just put some 117.5/120 mikuni mains in it and go.

 

[rasndas]

There is no popping or missing at high speed. That happened with the previously installed jets ( dyna jets) and they were too rich.

 

[Nicholaschase29]

The jets per my shop manual are 112.5 ( which is what I installed) and ran leaner than the dynojets. At least the missing stopped.

I would say 115 dynojet is LEANER than a 112.5 mikuni - so the stock ran lean but OK and the dynojet ran really lean.

DynoJets are leaner than mikuni jets with the same size stamped number in that range. put in Mikuni jets that are a few sizes that what the stock ones were. or put in dyna jets that are corrected for the flow difference.

DynoJet jets are marked according to the diameter of the hole in the
jet .. ie: DJ150 = 1.5mm and DJ175 = 1.75mm.
This is not true for Mikuni or most other OEM equivalent jets. This size
Mikuni jet, (N102.221 Super BN), is marked according to its' flow rate,
ie: 150 = a rating of 150 cc of fuel per minute.

 

[rasndas]

I am saying the dynajets were too rich because I ran the bike wide open and it would start to miss about 6000 RPM. I then took a piece of duct tape and closed off about 1/3 of the airbox opening. The missing then started about 3000 RPM. I then removed the tape and the top of the airbox and the missing stopped. I assumed after doing this that it was a problem of the jets being too rich. The dyna jets installed were labled as 115 but I have no idea if they had been drilled or messed with in any way by the previous owner. Thats when I installed the 112.5 Mikuni's.

 

[RacingJake]

Sorry if this has been covered before but I couldn't find a thread using the searh function. I have a stock 1983 GS1100E with the exception of a old vance and hines 4 into 1 exhaust.

Get some real jets like Mikuni 140's then come back and post the speeding ticket for 140 mph plus :twistedevil:

The best mod I ever did was to get rid of the dyno jets and needle's cause they will have you chasing your tail trying to fix a lean condition. Stick with Mikuni jets, go big for big power.