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Loss of Power at higher speeds and running lean

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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Hello fellow GS riders,

I recently installed a 2-1 exhaust, emgo pods, and new jets. The bike runs well, but there is a dramatic loss of power after about 55mph. She turns into a real dog after that no matter what gear I put her in. I checked the plugs after my ride today and they are bright white. I know this means lean and my theory is that she runs fine with too little gas at slower speeds, but when she is wide open trying to go faster she is not getting enough to drink. (just a SWAG at the problem).

Here?s some info on the carb work I did

Stock Pilot = 15 -- replaced with 17.5
Stock Main = 115 -- replaced with 120
I put one shim on the needle
Air screws are set at 2.5 turns out

I would like to do a more accurate plug read, you know cruising for a mile keeping a constant RPM and then hitting the kill switch. What are the specifics on this I have heard to keep the engine at 5000 RPM and also at wide open. So what?s the scoop on a good plug read since there seems to be a difference of opinions out there? :?

I have not balanced my carbs with a manometer because I don?t have one or the money to buy one. Could this be part of it as well?
Should I just get bigger jets and put them in with more shims on the needle? :idea:

Thanks in advance for all the help. I?m 22 and a senior in college and trying to teach myself about bikes as well as my classes and internship. I wouldn't even have this bike anymore if it wasn't for this wonderful forum.
 
Ok, I rejetted my 450 last week same mods as you. It's running awesome now. In my opinion you are jetted fine for the 2:1 exhaust but you need to richen up considerably for the Emgo airpods. You're running so lean I think a plug chop at this point is pointless.

Pilot Jet: 25
Main Jet: 130
 
Great, thanks for the info.

Is that the size jets you put in your 450? That seems like a huge jump, I am curious to what your MPG is?
What about shimming the needle, how many?

Many thanks!

Vox Teardrop said:
Ok, I rejetted my 450 last week same mods as you. It's running awesome now. In my opinion you are jetted fine for the 2:1 exhaust but you need to richen up considerably for the Emgo airpods. You're running so lean I think a plug chop at this point is pointless.

Pilot Jet: 25
Main Jet: 130
Click to expand...
 
my experience with pods at high speeds is they dont provide smooth airflow and jetting for high speed is a mess.
on my 750, i just gave up and went back to a stock airbox.
on my 1150, im still trying...

the messed up mixture might be due to your slides not raising all the way, that was the problem on my 750 at exactly the speed you describe. something about not enough vacuum to raise them. you might go to softer springs or block one of the air holes in your slides use epoxy, not silicone which will just get sucked out and into your engine.

please note that my advice is just something to try out, as i havent been able to get my bike to run right yet.

as far as plug chops go, pilot jet circuit controls mixture up to 1/4 throttle opening, between 1/4 and 3/4 it's the slide/needle/main jet, and between 3/4 and full it's the main jet. it has nothing to do with rpm, but everythign to do with throttle opening.

your best bet for smooth controlled airflow is to go back to the stock airbox though, you can get your setup to work but youll always have either a lumpy idle or a flatspot. theres a reason the engineers who built these things didnt put pods on...
 
Going up 15 from a 115 to a 130 is only around an 8 % increase if you look at it that way. 8% is a reasonable amount of bump to expect from the mods you have. Fuel economy may suffer slightly but you should get in the mid 50s per gallon anyway.

Better to be a bit rich than lean, lean will burn valves and melt pistons.
 
Thanks for putting it into perspective for me 8O :D

duaneage said:
Going up 15 from a 115 to a 130 is only around an 8 % increase if you look at it that way. 8% is a reasonable amount of bump to expect from the mods you have. Fuel economy may suffer slightly but you should get in the mid 50s per gallon anyway.
Click to expand...

Oh no! I just rode it 200 miles the way it is. How much damage do you think I did? #-o

duaneage said:
Better to be a bit rich than lean, lean will burn valves and melt pistons.
Click to expand...


gsBert,
Thanks for the info, I am glad to hear that someone else has had this problem. I have heard that pods are good for the strip and not the street. I don't plan on being at the strip with a 450 (I'd be laughed away). I will stick with the pods a while longer until I can get this sorted out or go crazy trying. There has to be a happy medium somewhere with regards to all around good performance...
 
200 miles is a bit far , but your probably OK since you did put a little bit larger jet in and your not wringing it out too much. Get it jetted before driving it anymore.

I am not a fan of pods, airboxes have purposes. Don't get caught in a bad rainstorm, pods don't flow air too good when wet.
 
I'll order the jets tomorrow. Should I do the pilot as well or is just increasing the main enough?

If I were to put the airbox back on should I return to stock jetting or leave the bigger jets in because of the 2-1 exhaust?
 
hipster said:
I'll order the jets tomorrow. Should I do the pilot as well or is just increasing the main enough?

If I were to put the airbox back on should I return to stock jetting or leave the bigger jets in because of the 2-1 exhaust?
Click to expand...

when someone with a similar setup reports success jetting I would do what he did as a starting point, change the pilot as well.

I think your 125/17/5 would probably work with the 2-1 and stock airbox, on a bone stock bike it is not a big deal. The carbs are more sensitive to the air cleaner because the carb senses the air flow coming in and the pressures that are present determine haow gas is coaxed into the venturi from the bowl. The exhaust scavenges the cylinder a wee bit better at high speed and that increases flow through the carb.

i had a 450 like yours years ago and was content with it the way it arrived from the factory. It is not a gsxr.
 
on my 750, i kept the stock jetting when i put a 4-1 on and it was ok.
the 1150 however with the same exhaust started running lean with the stock jetting.
it really depends on how much your muffler flows, unless it's a straight through glasspack, the stock jetting should be close to ok as a starting point if you're using a stock airbox, do a plug chop and see from there.

hey, try to get your hands on a gsxr400... personally, i'd sell my mother for one...
 
gsBert said:
hey, try to get your hands on a gsxr400... personally, i'd sell my mother for one...
Click to expand...

More info needed... when did they make these. What were the specs on them? Would it really be that much faster than the 450 I have now?

Cheers,

-David
 
they made them from the early 80s until last year that i know of.

they all have very good specs. the latest one(2004) is basically a 400 cc gsxr: dual disk front 4 pot caliper on each side, inverted fully adjustable forks.
they are 4 cylinder engines, make around 60+ hp and reach 100km/h in under 3.5 seconds...

so? better performance than your 450 i think?

of course, this is totaly off topic, and if you were to get yerself one, you need to keep the stock airbox on...

you might be able to import one through a friendly dealer or buy one in europe, an early 90's model will run you around 1000 pouds in the uk.
 
I get decent performance on my 450. I haven't shimmed the needle, thought I would try the rejet first and that has cured all my lean-running issues.
 
I ordered the jets this AM, should have them by the end of the week! 8)

I'll keep you all posted.

Thanks for the great info. I'll get this right yet, I know it! :D

Take care,
 
Re: Loss of Power at higher speeds and running lean

hipster said:
Here?s some info on the carb work I did

Stock Pilot = 15 -- replaced with 17.5
Stock Main = 115 -- replaced with 120
I put one shim on the needle
Air screws are set at 2.5 turns out
Click to expand...

On my '80 GS450 with the Mikuni carbs the factory service manual shows a spacer/shim in the slides which lowers the needle, leaning out the mixture. The PO had made a note that this spacer had been removed. When I cleaned my carbs I tried to raise the needles to richen it up and couldn't. The slides aren't built that way, they seem overly complex with their spring-loaded arrangement. Wish the needles had normal grooves and an e-clip. Maybe there are different carbs on your bikes but I don't think so. I bought a set of carbs on eBay from an '82 that were identical. My bike ran great at idle and wfo but seemed fuel starved at mid-throttle openings, hesitated and lost power. The only way I could richen it up without rejetting was to raise the float level some, which did the trick. I'm running stock everything from airbox to jets to exhaust. With the stock 16/45 gearing I can still get from 0-60mph in around 5.5 seconds, 5.3 was what Cycle World reported in their tests at the time. That equates to about 8500 rpm in third gear. Fast enough for me!

As far as balancing the carbs, I didn't mess with mine. I'll bet that the "bench-balancing" method of getting the clicks as the butterflies snap shut to be exactly in unison (sounding like one click) and using a .005 feeler gauge to measure the gap would work great on these mildy tuned engines.
 
Re: Loss of Power at higher speeds and running lean

I was able to shim my needles and successfully raise them. It took some thinking, but if you put the spacers below the spring then you will raise the needle. I also set my float heights to 26mm as that is what I found was recommended for my jetting changes.

BTW -- I have the BS-34 carbs.


IanFrancisco said:
hipster said:
Here?s some info on the carb work I did

Stock Pilot = 15 -- replaced with 17.5
Stock Main = 115 -- replaced with 120
I put one shim on the needle
Air screws are set at 2.5 turns out
Click to expand...

On my '80 GS450 with the Mikuni carbs the factory service manual shows a spacer/shim in the slides which lowers the needle, leaning out the mixture. The PO had made a note that this spacer had been removed. When I cleaned my carbs I tried to raise the needles to richen it up and couldn't. The slides aren't built that way, they seem overly complex with their spring-loaded arrangement. Wish the needles had normal grooves and an e-clip. Maybe there are different carbs on your bikes but I don't think so. I bought a set of carbs on eBay from an '82 that were identical. My bike ran great at idle and wfo but seemed fuel starved at mid-throttle openings, hesitated and lost power. The only way I could richen it up without rejetting was to raise the float level some, which did the trick. I'm running stock everything from airbox to jets to exhaust. With the stock 16/45 gearing I can still get from 0-60mph in around 5.5 seconds, 5.3 was what Cycle World reported in their tests at the time. That equates to about 8500 rpm in third gear. Fast enough for me!

As far as balancing the carbs, I didn't mess with mine. I'll bet that the "bench-balancing" method of getting the clicks as the butterflies snap shut to be exactly in unison (sounding like one click) and using a .005 feeler gauge to measure the gap would work great on these mildy tuned engines.
Click to expand...
 
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