the off idle bog

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alfred e numan

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Seems that all my carbs have an off idle bog- not really a bog, more like a hitch i suppose. When the carbs lsn is set at the ideal mixture at idle the bog is worse. I componsate -spelling-grrrr. by running too rich a mix - I bet nearly every one does the same thing. we all are loseing some power by haveing to take this band-aid approach to maskover this off idle hitch. I am new to these carbs- much to learn. On a Mikuni -Kehin equipped dirt bike carb- this is a tell tale sign of needing a larger low speed fuel jet- logically, this should be the correct diagnosis for our little fixed jet carbs.-Heres the problem.- There are 3 holes in the carbs bore. they operate in 2 ways- 3 diffrent stages. The Walbro on-line book explains this in farly decent detail.I am taking a wild guess here- the 1 st hole facing the air filter is where the idle fuel gets pulled out- the other 2 holes - well the walbro stuff i posted a while back can explain better than me. Me thinks- 1 or both of the 2nd 2 holes need to be increased in size. The ethanol mixed pump gas tends to go lean in engines- this will make the pesky off idle hitch worse. so will cold weather.- I am about to the point of buying a tiny drill set and see hot bad i can screw up a carb! lol! - Its the only way to find out-- Any suggestions out there??
 
Food for thought,check the carbs diaphram material,thier are 3 different colors of material.Blue lets the most fuel flow.sorry I for get the other two.
 
I do not know how to pull photos off a pdf file. So here is the link.-- http://wem.walbro.com/distributors/servicemanuals/ServiceManual.pdf Look at page 7. look at the idle circut then the part throttle circut. I think its one of the idle progression holes that need to be enlarged- guessing that it could be the center hole. Yea, I do have an wt 813. the problem with this accelator pump- It feeds fuel tru the high speed check valve. Too little fuel too late in the circut. - I know there are x-perts on these walbros out there- they never seem to post on this site or any other site that i have surfed. - I have 2 990s- 1 813 -1 668. The 668 has no high speed check valve. Gitzmo has the 990 for 35 bucks. The 990 is the carb to drill one of the idle progression holes out VERY slightly.-- if it screws it up?- just out 35 bucks i suppose.- Only one way to know---
 
Say Cordy! seen the solar flares lately?-- un real! - you can here these on the bands- we just had another flare this morning!--
 
recall the x47 flare a couple of years ago? we lucked out big time on that event-not earth directed.- it was a shot over the bow- if this would have been earth directed-- a kill shot for the electric infrastructure. scary. The flare this morning- very early i could here it soaking into the power lines- on 11 meters.- long time ago when the telegraph wires were strung cross country- there was a solar event strong enough to set paper afire when placed across the wires feed ing the key! we are all sitting ducks- anything solid state-- i keep my fingers crossed---
 
I think you will find it's not that the low or high speed is too lean, the motor runs fine in either end of the RPM range,the problem is that there is no fuel being added during the transition from low to high speed .for example in a automotive carb you have a, low speed /high speed /power /accelerator/circuits.

these carbs have 2 problems,first they can not increase fuel when load is increases at a given RPM (you need a vacuum activated power circuit for that).

second ,they have no means of supplying the extra fuel needed when the throttle is advanced (you need a accelerator pump for that )

you may want to try a variable venturi carb ,I am adapting one to fit my truck. WYK28b 247 . it has a metering rod that lifts when the throttle is advanced (has a rotating barrel like some glow engines)these carbs fall short in some of the same areas as the fixed jet carbs but the main jet is a metering rod that can be adjusted and does increase fuel flow when the throttle is advanced similar to a dirt bike ,anyway a little more advanced than the weed wacker carbs . Roger
 
thanks for the info. say, is the carb for your truck a ford product? going tru my motors manuals several years ago this type of carb caught my eye, very good idea! - years ago, Holly made a single barrel for the slant 6. holly #1920. had a really good design- economiser body. outstanding mileage out of these little carbs. - As for the r-cs, If we could find a tiny light weight fuel pump and a way to power it up, not run it off the battery, fuel injection!! carbs are old hat, a small control unit -ect-ect - then we would have something thad would run- no more chokes- a small starter injector just as a full size motor has- but on a much smaller scale--
 
oh- the wt 813 does have a acceleator pump- well sorta. its micky mouse cause what little fuel it does supply is not misted-atomised. it just slobbers out of the high speed check valve about 1 drop every tine the butterfly shaft is moved from idle to wot. too little fuel- too late.
 
alfred e numan said:
thanks for the info. say, is the carb for your truck a ford product? going tru my motors manuals several years ago this type of carb caught my eye, very good idea! - years ago, Holly made a single barrel for the slant 6. holly #1920. had a really good design- economiser body. outstanding mileage out of these little carbs. - As for the r-cs, If we could find a tiny light weight fuel pump and a way to power it up, not run it off the battery, fuel injection!! carbs are old hat, a small control unit -ect-ect - then we would have something thad would run- no more chokes- a small starter injector just as a full size motor has- but on a much smaller scale--
Click to expand...
I agree. Fuel injection would be incredible, especially if computer controlled. It would help in many aspects, performance, tuning, fuel consumption, ease of starting, ect. I would love to see power programmers for the RCs. Maybe we should evolve to 4 stroke first. :D
 
RCDAD said:
I agree. Fuel injection would be incredible, especially if computer controlled. It would help in many aspects, performance, tuning, fuel consumption, ease of starting, ect. I would love to see power programmers for the RCs. Maybe we should evolve to 4 stroke first. :D
Click to expand...
Yep, 4 stroke is the next stage. Then computer chip would make more sense :D
 
4 cycle

A four stroke can only produce 1/2 the power that a 2 stroke does. Unless its either supercharged or turbocharged. it would be a pig. way to heavy. There is another exception however. Its called a drum-valve engine. Honda Japan invented this in the late 80s. used on there F-1 program. it was mind boggeling once the bugs were eventually worked out. The intake-exhaust valves were replaced with 2 rotating drums in the top end. sorta like a 2 stroke spinning. belt driven with varable drum timeing. Then- the F-1 body changed the rules, what a piss$%. This was a 4 stroke that had little drag, no extreme valve spring pressures with less than ideal valve angles. It would rev to the moon-- Now most F-1 engines have replaced the valve springs with air valves. they still use the old fashoned reprocating valves - and have the same drag on the valve stems, guides-seals. Anyone here know a bigshot Honda employee?- If you do, Then tell them Honda should bring our little hobby engines into the late 80s with a drum valve engine.
 
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