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No power at/above 4,700 rpm 80' GS 250T

  • Thread starter Thread starter DragonMiata
  • Start date Start date
D

DragonMiata

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Hi guys I have a 250t BONE STOCK and It seams whether I am in any gear, or even neutral and revving it, The bikes slows through 4,700 rpms and then picks up a few thousand after that but still not as fast.
Current issue:
When I rev it in neutral: why does it slow down at 4,700 rpm then pick back up but lacking the power it should have. This is exactly what I feel when I am riding it. I take off and in every single gear it has absolutely no power after 4,700 until about 8k but even then won't pull like it should.
Carbs are clean (I shot cleaner through every jet and opening). Running premium fuel with seafoam. New oil, New spark plugs (NGK D8EA). No air leaks between the carbs and cylinder (sprayed while motor was running and no idle change). I want to say It's either the plugs are not correct and don't burn hot enough to burn off all the fuel at a higher rpm (but then wouldn't I hear back fires from unburned gas igniting on the headers?), or The bike isn't getting enough fuel (Sync the carbs maybe?)

Note: When assembling the carbs I noticed two hoses were never plugged in on the other end. I know one (from the left carb is the overflow). It looks like the overflow hose it missing for the right carb. But there is another on the right carb, inbetween the two and connects to a nipple aimed back at the rider and the other end looks like it was attached to something (its stretched out and looks like it sat on a nipple) But I have no Idea where. Looking at a Carburator Parts Chart it is hose number 55.


I will try running it in PRI to see if that helps but I don't think it is a petcock issue. It was doing this before and after I cleaned the carbs (I never removed the floats).

Thanks allot! :)
 
If you didn't remove the floats, you didn't clean the carbs correctly.

It isn't the heat range of your plugs.

On another note, running premium fuel has no advantage. You are just wasting money running anything over 87 octane.
 
The hose from tank goes to fuel t between carbs. The other hose on petcock (slightly smaller) goes to a nipple on right carb (?) on engine side of carb (this supplies vacuum to operate petcock). Other hoses aren't really for overflow, but to allow air to escape from fuel bowls as fuel pours in.
spraying carb cleaner, using Seafoam won't unclog the low speed circuits in this style carb unless you get lucky. There is a wide transition zone where the these circuits still must supply mixture before mains take over.
You likely need to fully strip and dip these carbs. Go here read this , for 450 but yours are likely similar

http://members.dslextreme.com/users/cbsaunders/gs/gs450_carb_cleaning_guide.pdf
 
OK Thanks guys i will try it again after work today and the only reason i ran premium was to help clean things out. I was only planning on doing one tank of it.
 
Ok so o have the carbs apart now and still nothing concerning. There are small mesh filters under the floats but other than that i still don't see any cause for concern. Removed everything. What about the shim height of the carb floats? Someone told me they might be a little to Low and it's not able to apply enough gas then.
 
These aren't lawn mower carbs, so you can't fully see the tiny passages forming the idle circuit and the transition to mid range. Spray/inspect all you want, but the full 24 hour dip is the best way to thoroughly clean these things .
 

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I just have one question before i soak it. How do i remove the long brass roofs with a fine hole in the to of them. They are in the bowl area and don't pull out of have any visual way to unscrew them. Thanks.

Also i tried it again but the problem is still there. I want to check the float bowl height. What size gap should there be
 
DragonMiata said:
I just have one question before i soak it. How do i remove the long brass roofs with a fine hole in the to of them. They are in the bowl area and don't pull out of have any visual way to unscrew them. Thanks.

Also i tried it again but the problem is still there. I want to check the float bowl height. What size gap should there be
Click to expand...

I have never removed the enrichment tubes. I just make sure they are clear after dipping them.

Have you read the info at the link that Tom sent you? It tells how to clean them correctly and how to set your float height.
 
DragonMiata said:
OK Thanks guys i will try it again after work today and the only reason i ran premium was to help clean things out.
Click to expand...

The only thing that "premium" fuel will clean out is your wallet. :-k
It does not have any extra cleaning power.

The "premium" part of it is the extra octane that resists self-ignition in the event the mixture gets too hot, which is usually caused by high-compression pistons or a large-diameter bore. Your bike has neither of them.

Also, along with the resistance to self-ignition, it burns slower, which means that it won't be done burning until the piston is well on its way down the cylinder, meaning that you won't get maximum push on it. Yep, that reduces your overall power. Any chance that sounds familiar? :-k

.
 
Higher octane is okay if you are running more advance timing. That said, I agree. Premium is a waste if you aren't tuned for it. It certainly won't have any cleaning effect.
 
GSCafe said:
Higher octane is okay if you are running more advance timing.
Click to expand...
For reasons I mentioned earlier, higher-octane fuel REQUIRES advanced timing to achieve proper combustion.

Many people are under the mistaken idea that "premium" fuel has more power (it actually has fewer BTUs per gallon) and advancing the ignition will add more power. What they fail to realize is that they are both "Band-Aids" that are necessary to cover for the higher-compression pistons, which are what is really making the extra power. Higher compression will raise the temperature of the mixture, possibly igniting it before the spark. "Premium" fuel is harder to light, so it is used to prevent pre-ignition. However, it also burns slower, so you have to advance the spark to get it all burned by the proper time in the piston's position.

.
 
Wow i have never heard of that premium thing but it makes compete sense and yes that issue sounds familiar. I'm going to drain the fuel and try it with regular gas. I did look through the link but i missed if skimmed over the float height part. Just trying to see how it would work without nipples to attach a hose to. I'll have it running good by tonight :)
 
JJ said:
Have you read the info at the link that Tom sent you? It tells how to clean them correctly and how to set your float height.
Click to expand...

Just went through it again. Nothing on setting float height. I know to use a hose on the nipple of the drain plug but these carbs only have 10mm bolts with no nipples... so I can't fit a clear hose to it and see where the level is.
 
Some members, including me, will use an extra drain plug and drill a through it and JB weld a piece of tubing or hose barb to it. Not an option if you don't have a spare though. You can do it with a screw but the threads are a little strange as they're .75mm fine pitch. You can also just shove a piece of tubing into the hole.
 
JTGS850GL said:
Some members, including me, will use an extra drain plug and drill a through it and JB weld a piece of tubing or hose barb to it. Not an option if you don't have a spare though. You can do it with a screw but the threads are a little strange as they're .75mm fine pitch. You can also just shove a piece of tubing into the hole.
Click to expand...

Thanks for the advice. I ended up taking them off and removing the drain bolt. Then I set it flat on top of a cup and let gas flow into the carb until it shut off. then I had my height. it runs allot better but I think I need to raise them a little more.

I also ended up adjusting the butterfly valves so they were actually the same angle. I do have a idling issue. It is either to low or too high, but mostly hangs. I am assuming this is from running lean, which would explain some power loss.

It looks like the previous owner played around with the air/fuel screws. What should they be set to for a stock set up. I.e. how many turns out from closed?

I sprayed some starting fluid around the two gaskets connecting the carbs to the block but the idle did not go up, so I'm ruling out that region for an air leak. I guess it would also help to adjust the tension on the timing chain. Would that or valve clearances cause my issue?
 
"also ended up adjusting the butterfly valves so they were actually the same angle"
better to use small drill bit or similar so that they are open the same tiny bit.
 
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