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Q about radial slide carbs

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

Anonymous

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You guys are going to see a lot of posts from me in the coming weeks. Im laid up cause I just had hernia surgery . annyway the Q is on my 77 750 if I open the throttle too far under 4000 rpm the bike dies and as soon as i let the throttle back it takes off again!! for all the years iv had my gs iv ben told that these carbs are like that i have to moderate the throttle myself? Well its not too bad if im riding myself and not in traffic--BUT tring to start out in traffic with 2 people really sucks!!!! It seams to me this is not right. I have tried many combos on the carbs and timing and cant change it. the mods I have are minor porting and 3 angle valve job(done by me) and a uni foam filter with the screen on the filter holder cut out Unfortunatly I still have the stock exhaust. IS THIS REALLY NORMAL????? :?
 
check your air mixture.. sounds as if its choking out... I had a honda do the same thing.. adjusted the idle screw and away it went...may be slightly different on the suzis I m about to find for my self.. but maybe that helps
 
Re: Q about radial slide carbs

NO, it is definitely NOT normal. My 79 750 has the same carbs as yours and it spools up like a turbine without ANY flat spots. The slide carbs are throttle position priority. When you twist the throttle, the slides raise and intake volume increases, but vacuum decreases. If vacuum decreases too much, then intake fuel supply is decreased also and your mixtures go very lean. The engine would go "flat" and decreasing throttle would then increase available power. I think your problem is the foam airfilter and not enough restriction for the stock jet sizes. Just to test my theory, why dont you try taking some aluminum foil and wrapping your aircleaner element so that you have blocked off about 1/2 of the surface area and try a test ride to see if it makes any difference. My feeling is it would not be a good idea to increase jet sizes because the stock mufflers are designed for a specific flow and if you were to increase intake and fuel volumes noticably, then logically, back pressure would have to increase. Too much back pressure is not a good thing for exhaust valves.

Earl



MR.ED said:
You guys are going to see a lot of posts from me in the coming weeks. Im laid up cause I just had hernia surgery . annyway the Q is on my 77 750 if I open the throttle too far under 4000 rpm the bike dies and as soon as i let the throttle back it takes off again!! for all the years iv had my gs iv ben told that these carbs are like that i have to moderate the throttle myself? Well its not too bad if im riding myself and not in traffic--BUT tring to start out in traffic with 2 people really sucks!!!! It seams to me this is not right. I have tried many combos on the carbs and timing and cant change it. the mods I have are minor porting and 3 angle valve job(done by me) and a uni foam filter with the screen on the filter holder cut out Unfortunatly I still have the stock exhaust. IS THIS REALLY NORMAL????? :?
Click to expand...
 
HHHMMMMMMMM Ill try that when im able to ride again Thanks!!!! And what does throttle position priority mean exactly???
 
With VM/mehanical slide carbs, It means YOU set the slide position with the throttle and the engine tries to catch up to that setting. With CV carbs, you request a throttle position and the engine gives it to you when IT feels it is appropriate. :-)

Earl





MR.ED said:
HHHMMMMMMMM Ill try that when im able to ride again Thanks!!!! And what does throttle position priority mean exactly???
Click to expand...
 
Depending on the engine configuration, everything starts to work at around 4000RPM. With full mechanical carbs you should be able to apply full throttle in this RPM range. I have 36 RS carbs and if I crack it at a low RPM it justs dumps tons of fuel in and it bogs. As long as it does not bog above 4000 RPM I would not worry about it, if it does your main jets are to big and you have to go down a size.

And as above you control the carbs, there is a bit of a learning curve if you are used to CV's. With CV's you can open the throttle wide open any time........the motor dictates the rest of the operation of the carbs by increasing vaccum and allowing the slides to rise as needed.

8) Andre 8)
 
So it iiiisssss normal for the bike to do that!!!!! :? I thought i was getting my leg pulled. I wish i did not have that indy car first gear it sucks to get going.
 
I just went through my first set of carb slides and had a spare set for parts. One set of them had a stop, an adjustable screw which you could adjust for a throttle stop. My assumption is that over cranking of the throttle will cause the problem you are describing. There are many people with more knowledge than what I have in these matters but this screw being adjustable is what I envisioned.
 
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