Does float height effect medium throttle?

[nabrams]

Hi All,

My 1980 GS450 hesitates when I try to accelerate and then eventually takes off very fast. I've checked for air leaks at the intake boots by spraying gumout all over that area while the bike idles. The idle does NOT change even a drop. When I cleaned the carbs, I may not have measured the float height correctly.
It idles great (smooth as silk at 1100 RPM). Does that prove that the float height is correct? I really don't want to wrestle those carbs out again.
If the bike idles OK, can float height have any effect on mid-range power?

Thanks

 

[earlfor]

Re: Does float height effect medium throttle?

If float heights are set too high (fuel level in the bowl is too high), the engine will run rich. If the fuel level is too low, the engine will run lean. Usually, (to a point) a richer mixture will produce a smoother idle and most bikes will idle just fine with the choke partially engaged. So yes, incorrect float height will cause a change in mixture. You didnt say what color the plugs are burning.
Is your bike fitted with slide type carbs or CV's?

Earl

Hi All,

My 1980 GS450 hesitates when I try to accelerate and then eventually takes off very fast. I've checked for air leaks at the intake boots by spraying gumout all over that area while the bike idles. The idle does NOT change even a drop. When I cleaned the carbs, I may not have measured the float height correctly.
It idles great (smooth as silk at 1100 RPM). Does that prove that the float height is correct? I really don't want to wrestle those carbs out again.
If the bike idles OK, can float height have any effect on mid-range power?

Thanks

 

[nabrams]

Earl,

Thanks for your response. My plugs are a very light gray color. Based on the fact that my bike idles very well, I'd guess the floats are set OK, and that the light color results from the off-idle lean-ness (thus, the hesitation).
But, maybe the float level affects off-idle as well. What do you think? The slides does not go up through mechanical linkage, but rather through vacuum. Do I have CV carbs then? I don't know what CV stands for. Perhaps I need to raise the needle using a washer (as suggested in other posts). If so, how thick should that washer be? It wasn't clear to me from those other posts.

Thanks in advance for any suggestions.

Nathan

 

[focus frenzy]

you might be a touch lean, it would be best to make sure the float level is set correctly before changing any settings.

you do have CV type carburators, CV stands for Constant Velocity, they maintain a constant air flow speed across the main jets.
to rase the needles you will need very thin washers, on the order of about the thickness of a match book cover.

 

[Billy Ricks]

I picked up a package of nylon washers at home depot that are a good compromise. The package shows they are #4 2B size washers.

 

[earlfor]

I would pull the carbs and check the float levels to be sure they are set at the correct height. The light gray color of the plugs is indicative of the mixture for the speed of your test ride. If the float levels are found to need resetting, I would test ride the bike again to get a plug color reading before I would consider changing needle positions. I dont like to run with lean/gray mixtures and prefer plug colors in the medium tan range or even to slightly brown.

Earl

Earl,

Thanks for your response. My plugs are a very light gray color. Based on the fact that my bike idles very well, I'd guess the floats are set OK, and that the light color results from the off-idle lean-ness (thus, the hesitation).

Nathan

 

[KEITH KRAUSE]

I measured the spacer that is used to make '1/2' clip position adjustment.
.023''. From my Dynojet kit.

 

[Anonymous]

I picked up a package of nylon washers at home depot that are a good compromise. The package shows they are #4 2B size washers.

good info Billy thanks

 

[Don Lobacz]

When you cleaned the carbs, did you run a soft copper wire through the pilot jets to make sure they were completely open? Did you remove and clean the air/fuel screw assembly? Did you scrub the needle jet and the jet needle? These are the 3 most common causes of midrange hesitation that I have seen (with the airbox working correctly).

 

[nabrams]

Hi All,
I hope to get some time this weekend to try all the great suggestions out.
Don,
I removed the pilot jets and srpayed them through with carb cleaner. Initially, the stream coming out the other side was not as strong as the stream going in. After 20 seconds of spraying, the stream coming out was just as strong as the one going in. I was wary of sticking wire in there for fear of damaging them. The needle jets and needles were spotless after I cleaned them. I did not take off the tamper-proof caps for the air screws, so I never cleaned them. However, I'm worried about ruining the screw heads while drilling in the cap. I partially ruined one that way on a spare carb I have (has more mileage on it). On that older one, the screw and passage was spotless, so I figured mine must be that way too. I've got the original airbox with a replacement foam element that fits well. The lid on the airbox may have some tiny air leaks around the edges due to age. Could this be the culprit? It would surprise me greatly to learn that such a tiny difference in airflow could cause this problem.

Thanks again,

Nathan

 

[Anonymous]

Flat spot

Flat spot

One other thing you might want to look into, since your bike is a 1980 i would think seriously about upgrading your ignition coils. Stock coils over a period of time tend to loose energy and become weak. I went to ACCEL super coils and lordy did my 1980 GS 750 come back to life. I also had a flat spot off idle and the coils pretty much cured that problem. Stock coils are rated around 30 kv where the ACCELs are around 50 KV The ACCEL coils come with new wires and match this system with some good plugs like split fires or a good platinum plug. Watch the heat range on the plug too. Also with a hotter coil open the gap up slighty over the factory settings, .46 to lilke .48 or a tad more, this makes these hotter coils fire more of their energy.

Since you said your plugs are a light gray color that indicates a good fuel air mixture, though if you want to check your plugs correctly this is want you need to do. Take your bike out on a good long stretch of open road and get it up to around 60 mph and hold that speed for about 3-5 miles, then pull in the clutch and kill the motor with your kill switch, pull over and let the bike cool for about 30-45 mintues, then pull your plugs, this will give you a good true reading on your fuel air mixture. the plugs will still be on hot side so becareful pulling them.

Switching out the paper air filter to a K&N air filter will give it a slight boost also.

Okay hope this all helps.

bill

 

[Anonymous]

ooops

ooops

Got ahead of my self in my first response, the light gray color is a sign of off idle leaness, which most 1980 GS bikes are famous for, and yes a light brown or orange color is what you need to look for in the plug test i mention in the first respone.

As for the jets, you can get new ones from a dealer they just order from the carb maker, i have several sets for my bike since i had to rejet it when i put on a pipe, K&N air fillter and the hotter coils on my bike, leaned it out big time so had to install bigger jets to get the fuel air mixture correct. Oh yeah change the carb rubber boots to the head, they are cheap and easy fix when you have the carbs off. 22 year old rudder can have cracks and splits in them.

One more thing make your carbs are in sync. Off sync carbs can cause some headaches.

Sorry for the mistake.

bill

 

[nabrams]

Well, I pulled the carbs. The float height for the right carb was about 1 millimeter below the lower limit. The left was at the lower limit exactly. So I set both to the upper limit (the range from lower limit to upper limit is about 2 millimeters according to the Clymer manual) to give a richer mixture. I also sealed the tiny air leaks on the airbox lid with silicone. The problem still persists. I'm not going to pull the carbs again to raise the needles (I've already pulled those carbs three times). Maybe I'll do that some other time. I have a work-around that works OK for most gear/RPM combinations. I limit the airflow into the airbox using folded cotton t-shirt material at the mouth of the airbox inlet (on the lid). This works OK till I get up to 60 MPH in fifth gear or 65 MPH in sixth gear. In those cases, I get hesistation as well, but it seems to last for less time.
I also tried running with a bit of choke (attempting to richen it), but this does'nt seem to work well for as many gear/RPM combinations as my cotton t-shirt trick.

 

[Anonymous]

One pull that t-shirt out of the air box, your straving the engine for air and thats not helping anything, its just a band aid. Your engine doesn't come on to the cam unitl about 4,000-5,000 rpm and it needs the air flow. At those higher rpms, your restricting the air flow way too much. Put a K&N air filter in. step up the jets a size or two. Set the floats inbetween upper and lower levels, make sure the carbs are in snyc. Two, with CV carbs when the choke is on and you roll on throttle it over rides the choke, so your not getting anything there, and stay with the stock gearing its fine for street riding.

And try the other things i mentioned in the previous response. Dealing with your problem is a process of elimination. Just gotta deal with it. You'll hit the right combination sooner or later. The end result is a better performing bike.

On the other hand you might want to consider stepping up a to bigger bike and make all this really worth the effort and exspense and have something that will be a bit more fun to ride.

 

[nabrams]

It turns out I don't need to remove the carbs in order to raise the needles. When my fuel tank is removed the carb tops are are accessible. So I rasied the needles about 1 millimeter each and removed the t-shirt from the airbox to test results. Now the hesitation is almost completely gone for all gear/RPM combinations. In fact, it's so minimal that I think I'm going to just ride the bike with some fuel additive for a few tanks to see if that will be the finishing touch needed to completely solve the problem. Maybe I won't have to pull those carbs again after all. I want to avoid all the effort of re-jetting till I have more time to experiment.
Wish me luck.
Thanks for all the great suggestions.