Mercarb idle speed screw and adjustment

[jonny rotten]

I don't think I've ever written a post like that.

1. Warm up the engine.
2. Check timing is correct.
3. Adjust idle SPEED to spec.
4. Moving idle MIXTURE screw/s 1/4 turn at a time, turn screws CW (leaner) until engine slows slight. Turn screws CCW (richer) until engine speed picks up, then slows again.
5. Set mixture screws between these points. If in doubt, err on the side of richer rather than leaner.
6. Adjust idle speed to spec. (It may have changed in the process of adjusting the mixture)

Chris.

I thought this had to be done in the water idling in forward gear? I see no mention of that. Is that correct?

 

[Kubaat3lover]

They will be a response, you just may now be able to detect it.

Ok I will monitor the RPMs on the tacho, ive got the laser one
the one on the boat overreads around 100rpms @ idle
And ofcourse all the settings, idle , mixture with unhooked throttle cable at carb?

 

[achris]

I thought this had to be done in the water idling in forward gear? I see no mention of that. Is that correct?

Idle SPEED yes, idle MIXTURE can be done in neutral.

 

[Kubaat3lover]

Hello Chris again,
Setting Base Timing mode, it’s around 10* BTDC.
Set the rpms @ 580rpms @ forward idle, the
Turned mixture CW till Engine rumbles, Then CCW until highest I have reached highest RPM. I hope it’s the right spot. Here are my plugs no3 and 4 after 2 hours of use : what do you think? Little lean? Good?

 

[achris]

They are look good...

 

[Kubaat3lover]

Thank You I owe You a beer! Please tell me how I can thank You for your help ?
I was wondering if they are a little bit lean, you said in your posts to be on the richer side (safer) so dont know what to do now but Im rookie and Wish to get the advice from more experienced guys

 

[Kubaat3lover]

Last winter carb rebuil, mixture idle screw set,
i was struggling with Choke but finally its set more leaner,
plugs are brown/tan - perfect
Engine starts and runs perfect when cold / hot
what I ve observed:
Engine cold, 2-3 full throttle then 1/4" forward, starting the engine
Idles great and starts right up every time.
Leaving the nes wake zone from marina for 3-5minuts and at about 900-1000 rpm's @ forward idle, rungs great. Give it some WOT from and and it runs ok but then around 1300-1500rpms wants to bogg, RPMs drop to 1000 then it accelerates and runs great, it happens only when 1st start of the day, then it runs like a kitten.

 

[Scott06]

Last winter carb rebuil, mixture idle screw set,
i was struggling with Choke but finally its set more leaner,
plugs are brown/tan - perfect
Engine starts and runs perfect when cold / hot
what I ve observed:
Engine cold, 2-3 full throttle then 1/4" forward, starting the engine
Idles great and starts right up every time.
Leaving the nes wake zone from marina for 3-5minuts and at about 900-1000 rpm's @ forward idle, rungs great. Give it some WOT from and and it runs ok but then around 1300-1500rpms wants to bogg, RPMs drop to 1000 then it accelerates and runs great, it happens only when 1st start of the day, then it runs like a kitten.

I also get the same with my Edlebrock 1409. Probably not the answer you want to hear but I suspect the passages in the accelrator pump circut or venturis dry out and have no gas until you accelerate and run some through. If it works really well in all other phases I would leave it allone or accelrate more slowly on first hit of the day. once I get it above oplanning speed same thing as you runs perfect...

 

[Kubaat3lover]

I have 2 steady streams when pumping the throttle, you said about this venturis that dries out, why that happens?

 

[Scott06]

I have 2 steady streams when pumping the throttle, you said about this venturis that dries out, why that happens?

I dont know this is only my theory which may be wrong

 

[Kubaat3lover]

Again.. Today after sitting 1 week ive got blackish smoke coming from the exhaust and running rough ,I think its running too fat. It happens only when 1st start of the day only, im wondering if its issue with the choke, need to lean it more or maybe too much float drop (?)

 

[Kubaat3lover]

@achris ??

 

[achris]

Sounds like you can afford to move the choke to a leaner setting...

 

[Kubaat3lover]

I will lean more but... do you know what can cause this rich setting? Plugs are brownish/tannish. But runs nice when warm, full @ WOT.. only issue when cold 1st start of the day. May the float drop will be wrong ? I’ve new brass float but set to the manual

regards

 

[achris]

It appears that an adjustment is necessary. Why? Your engine doesn't need as much choke as normal. That's not good, or bad, it just is.... Don't read anything else into it..

Chris.....

 

[Kubaat3lover]

Thanks Again here Chris, Ive set it much leaner and runs smooth when cold!
I think my spring coil in thermostat may be just worn and when lean the spring is very weak... will figure it out soon, again Thanks a lot
Regards from Europe