float height, rich in mid range 5000-7500

[angrypants]

ok so my step sons GSx250et, which in think is the same engine as the gs250t ( the 4 valve per cylinder engine with bs30ss carbs).

ive been trying to solve a flat / weak spot in the acceleration between 5000-7500 for a while, before and after that rev range it goes great, idle sits perfect no hang no rise. it actually pull surprisingly hard after 7500-8000 is past redline very wuick... its just the waiting from 5000 to get that which is annoying and dangerous of trying to overtake

what ive done new rubbers airbox sealed, carbs dipped twice, jets cleaned dipped and ultra sonic, compressed air blown through passage ways etc etc actually put in new OEM mains as the exiting had screw driver damage, all new gasket etc, new OEm filter oiled and squeezed out well, valve clearance set, mech advancer checked with strobe , plugs changed, petcock rebuilt and working correctly. needle is adjustable i did raise it but made no difference maybe worse, i put it back to stock. everything is stock except the muffler are a reproduction same style as OEM long ones.

plugs show rich, but i still kept expecting a lean condition as that seems to usually be the issue. i was stuck in rev range yesterday and pull the choke on and it got worse, choke off and it went a bit better, i did this twice up a long gradient, so that would spell out rich yes?..so before i go and lower the needle (does anyone ever lower the needle on a stock GS??) , let me ask about float height, as i have just remembered something.

when purchased we cleaned the carbs properly and followed the other must doe recommendation form this site , ( at this point the bike was hardly ridden so no idea if this flat spot was happening then). i "now" recall today i had to reset the float height higher that it was set. it seemed surprisingly out .. i recall that thought. As was / is the general consensus, i measured from the surface the gasket sits on with no gasket and never thought about it until this morning. see below the suzuki manual & the haynes, both showing to measure "A" form what appears to be the top of the carb lip NOT the mating surface. The suzuki manual just says measure 'a"
it does have the warning about removing the gasket in both - and haynes does refer to the mating surface, but both pics don't show that- other manuals from suzuki definitely have the lower "A" line below the physical /visible top of the carb body... ive check and found this in older manuals and newer manuals -- so im thinking why would this pic be wrong

im thinking that if indeed the picture is correct then i have given a lower relative float height measuring from the gasket surface and thus a higher fuel level, as i understand it fuel level is an overriding setting, could this be the ghost i have been chasing ? could a greater fuel level cause this flat spot ?

im going to go out and find out by testing it.. just thought i'd see what people thought

[Steve]

Yes, an incorrect fuel level will change the mixture in ALL the ranges. It will be easier for each of the jets to draw fuel from a higher level, so pilot, needle and main circuits will ALL be running rich.

Your pictures are too small and too fuzzy to read, but it's trying to show you that you measure to the top of the curved section, NOT the top of the step. That error can account for several milimeters of fuel level difference.

If you want to double-check, it's best to rig a fuel line to a drain screw adapter to see what the actual level is when the carb is upright and has fuel flowing through it. The float level usually gets you into the ballpark, the fuel level check is ideal.

.

[angrypants]

Yes, an incorrect fuel level will change the mixture in ALL the ranges. It will be easier for each of the jets to draw fuel from a higher level, so pilot, needle and main circuits will ALL be running rich.

Your pictures are too small and too fuzzy to read, but it's trying to show you that you measure to the top of the curved section, NOT the top of the step. That error can account for several milimeters of fuel level difference.

If you want to double-check, it's best to rig a fuel line to a drain screw adapter to see what the actual level is when the carb is upright and has fuel flowing through it. The float level usually gets you into the ballpark, the fuel level check is ideal.

.

thanks for the quick reply Steve - new pic uploaded to original post , photo bucket is being a pain .you should be able to see the detail here and compare with a photo from a similar vintage suzuki manual

my question is not the top part of measurement A but the bottom.. i.e on the 250 pic you can see its the top of the lip, not the mating surface, as opposed to this photo below from another 1980 Suzuki manual for a gs 450 which clearly has the measurement level below the lip where the mating surface would be.. i have several others a 1978 gs1000 manual clearly has the bottom line of "a' below the top lip. do the Japanese make mistakes like this?? i admit i have found a couple on parts manuals.
measuring from lower would give me a greater fuel level wouldn't it?

[angrypants]

ps i have a new drain plug on order so i can drill it and make the fuel measurement gauge, to then check it that way

[londonboards]

I would suggest taking the air filter out completely and doing the same runs as you have described. Does it still have the flat spot and are the plugs still showing rich? Maybe the air filter is choking the motor - too much oil in the filter?

You do have the correct size Mikuni jets in there, don't you?

A lot is made of float heights but have you even seen inside a float bowl when you are riding up the road at full chat? (see some transparent Lectron carbs). It's a perfect storm in there! And there is quite a range of acceptable float heights, according to the manual, so it can't be too too critical. Sure, if there were way out, or the floats aren't actually closing the valves when the bowls are full.

What surprises me is the amount of adjustment you had to make to put them back into range. Why would they be that far out in the first place? Did the bike go OK before you adjusted them? The chances that someone has previously adjusted them that far out, are, I would suggest quite slim. So check you have measured them correctly. They may have been OK in the first place.

In general, I would say there is a greater probability that the jets are incorrect or the air filter is choking the motor. The tang on the float adjustment should only be out by about .5 mm either way of flat. Anything above this, then you have either measure incorrectly or the spring in the float needle is goosed and they need replacing.

[angrypants]

I would suggest taking the air filter out completely and doing the same runs as you have described. Does it still have the flat spot and are the plugs still showing rich? Maybe the air filter is choking the motor - too much oil in the filter?

You do have the correct size Mikuni jets in there, don't you?

A lot is made of float heights but have you even seen inside a float bowl when you are riding up the road at full chat? (see some transparent Lectron carbs). It's a perfect storm in there! And there is quite a range of acceptable float heights, according to the manual, so it can't be too too critical. Sure, if there were way out, or the floats aren't actually closing the valves when the bowls are full.

What surprises me is the amount of adjustment you had to make to put them back into range. Why would they be that far out in the first place? Did the bike go OK before you adjusted them? The chances that someone has previously adjusted them that far out, are, I would suggest quite slim. So check you have measured them correctly. They may have been OK in the first place.

In general, I would say there is a greater probability that the jets are incorrect or the air filter is choking the motor. The tang on the float adjustment should only be out by about .5 mm either way of flat. Anything above this, then you have either measure incorrectly or the spring in the float needle is goosed and they need replacing.

jets are stock and clear genuine mikuni... im wondering if the needle is worn and or the needle jet is worn
im just going to do some plug chops now.. will take or dislodge the filter a bit and see what that does. as for the float height i check the second time i dipped and cleared the jets etc and i had to adjust them again too so ??? still same symptoms ... we are not sure how it went before we did the carbs the first time as it wasn't running great as they were full of gunk, and hardly ran . all is very clean ive got a gs400 and done those carbs twice and these twice in the last 18 months. dipped for 12-18 hours, poke out the passage ways with stout fishing line and or copper wire , spared through all passageways to ensure clear, ultra sonic clean the jets too. the bike runs gerat in all areas except that middle part -- full throttle at 5500-7500 ish and it just is weak then it takes off like a bull to 10000 .
anyways bets go and test the thing ! i'll report back
thanks

grant

[angrypants]

left cylinder - these were very clean as before the run no soot anywhere and only a off white slight color to the insulator . I ran at the flat zone about 6000 rpm with WOT at up an slow incline for 1/4 mile cut the engine neutral and pull over ( is 1/4 mile far enough? )

[angrypants]

right cylinder

[angrypants]

I should add that I can roll on upto that 5-6k rpm with about 1/3 throttle and all seems good wont really get past that area with that little throttle though... but then if I got to full throttle it labours through that range until maybe closer to 8k and then it's like 2 stroke power band coming in

[angrypants]

ok so my step sons GSx250et, which in think is the same engine as the gs250t ( the 4 valve per cylinder engine with bs30ss carbs).

As was / is the general consensus, i measured from the surface the gasket sits on with no gasket and never thought about it until this morning. see below the suzuki manual & the haynes, both showing to measure "A" form what appears to be the top of the carb lip NOT the mating surface. The suzuki manual just says measure 'a"
it does have the warning about removing the gasket in both - and haynes does refer to the mating surface, but both pics don't show that- other manuals from suzuki definitely have the lower "A" line below the physical /visible top of the carb body... ive check and found this in older manuals and newer manuals -- so im thinking why would this pic be wrong

im thinking that if indeed the picture is correct then i have given a lower relative float height measuring from the gasket surface and thus a higher fuel level, as i understand it fuel level is an overriding setting, could this be the ghost i have been chasing ? could a greater fuel level cause this flat spot ?

im going to go out and find out by testing it.. just thought i'd see what people thought

so i found another suzuki manual see below. Same engine, same carbs - USA model gs250T Vs gsx250et.. ..but the picture shows the measurement of 'A' being from the mating surface.. only the needle is noted as different and one needle jet - the gsx250 has different needle jets in left and right crab?/ - so i ti'd bet the pic above in the Suzuki gsx250 manual is wrong -- the wording of where to measure and the warning about removing gasket is identical - weird they made that error and even more strange you'd think they would just use the same pic?

so i'll guess there no need to worry about float height i set it as below... with the left and right carbs have a different needle jet, i may have swapped them over -- out come the carbs again... after i go for a run today with out the air filter to see whats whats

pic for comparison form thegs250T manual ( sam carbs same motor) .

PS was 1/4 mile to 1/3 of a mile up a slow hill enough to get a read on those plugs or should i find a longer run ?? thoughts

[angrypants]

UPDATE:
removed air filter... was an improvement - its still there but not as bad or in a lesser range.

my spare bowl plug turned turned up today (Along with the last of the gs1000 parts happy happy ). so i will drill out the old plug and make a fuel level measure to sort that question out ...and on the weekend will drop the needle a notch and see how that goes

the filter was little oily but would not squeeze any drops so i put it between some paper towel and stepped on it to remove some of what is there