Hesitation

[kevin2502000]

Need some ideas about a flat spot between 2k-4k. Completely stock, recently rebuilt and cleaned carbs. Revs nicely without a load, has a little balk under a load between 2k-4k. I thought maybe a little dirty carbs yet but it seems to do it after it warms up and not so much when it's cold. Haven't run much gas through the carbs yet so I'm gonna do that and see if it improves first but would like some brain storming. (90 750) I synched carbs and set floats etc.

[Court93kat]

Have you got any Techron or STP fuel treatment in the tank? Might be something small enough left over from the cleaning that will take care of it. Only 1/3 bottle to a full tank though. Hopefully that might help out.

[IndyGunner]

did you readjust your AF mixture screws properly? Seat them and untwist 2.5 turns out.

[gazoo]

i had a big flat spot and today i finally decided to take the carbs off and fix it . the bike would bog like something was stuck ( a slide ? ) and i had to rev to clear it up . also the idle would be fine for a while then after a short ride raise up 500 to 600 rpms above normal . i removed the float bowls and set the height to 15 mm .they were not all the same , i set them according to the haynes manual . i know there are other methods . i then checked the slides and they were ok .easy movement no hanging up . i put everything back together and the thing runs beautifully !! not one problem all afternoon . life is good again .

[ICEG]

af screws

[kevin2502000]

Yes, af set at 2.5.

[gazoo]

yep , mine were set at 2.5 so i didnt touch em . basically everything you need to know is here on this forum . just take your time and do it right .

[md86]

Float height ?
Low end (full throttle / 2k-3k)
Step 1 (Best Main Jet) and Step 2 (needle height) must be selected before starting step 3!

• • Float height (AKA fuel level & how to..)
  
  
• To get best low-end power, set float height (fuel level) so that the engine will accept full throttle, without missing or stumbling, in 2nd gear from 2.5k to 3k rpm at minimum.
  • Float heights, unless otherwise specified in the installation guide, are measured from the "gasket surface" of the carb body to the highest part of the top of the float - with the float tang touching but not compressing the float valve spring.
  
  
  • If the engine has a "wet" rhythmic, soggy area at full throttle / 3k-4k rpm, that gets worse as the engine heats up, lower the fuel level by resetting the float height 1mm greater (if the original was 13mm - go to 14mm). This will lower the fuel level, making full throttle / 2k-3k rpm leaner.
  • If the engine is "dry" and flat between 2k to 3k rpm, raise the fuel level.
  • Example: change float height from 15mm to 14mm to richen up that area.
  • REMEMBER, since the main jet WILL affect low speed operation, the MAIN JET has to be within 1 or 2 sizes of correct before final float setting.
  
  And now for the how-to.... http://771doug.netfirms.com/float.html

[Kreylyn]

2-4k is the transition from the pilot jets to fully the main jets. I would check the needle position (shim or lower the eclip), and make sure your diaphrams do not have any holes. Also check the vacuum holes on the bottom of the slides for uniformity between the slides. Are all the holes drilled, each has 1 restrictor, or they have restrictors in all the holes.

Have the emulsion tubes been pulled and inspected?

Krey

[waffenampt]

clean air filter?

[kevin2502000]

New air filter, OEM, new plugs, valves adjusted, synched. Carbs taken apart and cleaned and all orings replaced. Even though I've had these carbs apart MANY times, it's POSSIBLE I may have inadvertently put the jet needle together wrong on one of them, I'm not ruling anything out. I did set my floats at 14.6 but that is exactly how it sounds according to MD's chart. If I get ambitious and it doesn't get any better after a few tanks I might lower them. Never had a problem before after a cleaning so it kinda puzzled me. Also bike only has 16k on it so I shouldn't have any worn carb parts yet. My diaphrams do lift with vaccum and don't stick. Thanks.

[Kreylyn]

New air filter, OEM, new plugs, valves adjusted, synched. Carbs taken apart and cleaned and all orings replaced. Even though I've had these carbs apart MANY times, it's POSSIBLE I may have inadvertently put the jet needle together wrong on one of them, I'm not ruling anything out. I did set my floats at 14.6 but that is exactly how it sounds according to MD's chart. If I get ambitious and it doesn't get any better after a few tanks I might lower them. Never had a problem before after a cleaning so it kinda puzzled me. Also bike only has 16k on it so I shouldn't have any worn carb parts yet. My diaphrams do lift with vaccum and don't stick. Thanks.

I'm not saying you put it together wrong.

But, just a possibility of several factors....

1. Carbs wear, especially the CV carbs like the pre kats at the needles and emulsion tubes.
2. Carbs get dirty. (I would assume this happened to you and the reason for cleaning them to start with?)

If the carbs wear, they run a little richer with the emulsion tube holes getting larger, and the needles wearing thinner. As the carbs get dirty, they lean out. If both happen, you may not notice the wear, as they dirty actually keeps them running about the same...

Then you cleaned them, removing the varnish coating, allow them to suddently go very rich. If you have a jetkit needle installed, you can counter this by raising the eclips towards the top of the needle.

If your stock needles and jets..... you may need to verify if there is wear on the emulsion tubes or needles, and replace.... or get a jetkit (won't have emulsion tubes) depending upon your needs.

In general, hesitation at the 3-4k range means the needles are running to rich and should be adjusted to lean things out with a jetkit. My explination would be a possible reason the stock system would act this way on a used bike.

I don't remember if you have a jetkit or not and feeling lazy atm to go look...

Krey

[md86]

Are all the holes drilled, each has 1 restrictor, or they have restrictors in all the holes.

Have the emulsion tubes been pulled and inspected?

Krey

DJ claims you can leave out one for "hard street riding" . Me , I filled them in with JB and drilled them back to close to stock size .

[kevin2502000]

OK guys got it figured out. It was my floats set WAY too low (under 14.0 is out of spec) which made it run very rich. What happened was I replaced the o-rings on my float assembly when I re did the carbs. I was one size too big on the rings and it wouldn't let the float seat. I went down a size on the oring and had someone help me hold the assembly flush with the carb body. The bowls will keep it in place when tightened down. I think before I wasn't getting it pushed down far enough making my reading way off. The worst one was probably 1/4" off. Surprised it didn't overflow my bowls. Anyways it purrs now, haven't done a road test but I can tell it is running alot better. At those lower rpm's it was loading up with fuel causing my hesitation. MD wins the prize

[md86]

MD wins the prize