carbs setting up

avon5.4 · 14 March 2007, 18:56

how do you set the carbs up on a 3 cylinder engine, in the manual it says turn out 1.5 turns on the air screw, then is it left in then positions and screw each idle screw till each carb runs ok i/e make each carb idle speed diffrent so as to balance out. is it also true that when a cylinder is running ok you can pull off the ht lead and it should make no diffrence to the engine,
hope this makes sence as its my last resort , i took the engine to a mariners shop and i got the whole engine back in bits and i dont want to go through it again . cheers if you could help me andy.

ian parkes · 14 March 2007, 20:20

the pulling off an Ht lead is certainly not correct . If pulling off the lead makes no diffrence then that cylinder wasn't firing in the first place .

Are you wanting to get the carbs balanced , because they have been taken apart ?

avon5.4 · 14 March 2007, 20:54

we can get it to run but it seams to be running hi then low i/e searching , i took to boat yard and he cleaned them then put back together but found another problem , one minute it could be ticking over at 1200 then it could drop to 900 rpm it never stays in more or less the same range. weve messed with a colour tune and the screws ended up allover the place so i was just woundering if the settings in the manual have to stay around that then ajust the tickover screws on each carb to get it to run reasonably well , all i want is a decent reliable setting that i can reliey on when out on the water, and for it to start every time,

bobbyjoeufb · 14 March 2007, 21:17

Rough Idle Could be-

Old or Contaminated Fuel
Fuel Pump Malfunction
Plugged Carb Jets
Improper Carb adjustment
Air Leak in Fuel Hoses
Improper Choke Adjustment

I have just balanced the Carbs on my Tohatsu, it invovled ensuring that all 3 throttle butterflies are fully open at WOT, also the same for the Choke Butterfiles. As for the fuel / air screws I set these all at 2 and half turns out.

Might be an idea to get hold of a good shop manual like Clymer or take the engine to a good dealer.

Hightower · 14 March 2007, 21:29

A manual is a definate way forward.

Hunting is usually caused by an air leak somewhere. Check all the hoses and gaskets. It can also be caused by a blocked idle jet and incorrectly balance carbs.

You won't be able to balance the carbs without a vacuum gauge unless you're very experienced and can tell by inserting a tube into the throttle and listening to the other end by ear.

My advise is to go to a recommended outboard shop.

Biggles · 14 March 2007, 21:59

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http://forums.iboats.com/

fast fred · 15 March 2007, 13:03

you got to balance them, so they are timed the same. turn the low speed mix screws in till they stop, then back them out to what the book says.

ware di you get the carbs?

fast fred · 15 March 2007, 13:17

one carb is the leader, the other two follow, the follow two got a screw on the linkage plate, some times it's reverse thred, leaders got the idel screw,

back idel screw out, till carb is totaly closed, go to next carb loosen linkage plate screw, ( carb closes by it's self ) retighten , go to last carb, repete last step.

now thay are timed, or balanced

avon5.4 · 15 March 2007, 17:52

fast fred cheers for that info but weve allready done that , i/e the middle carb controls all 3 but the top and bottom can be ajusted independently as well , the carbs a genuine selva one that came on the engine, weve took of the air intake housing to make sure all butterflies were shutting at idle unscrewed out the 1.5 turns as in manual but it still wont settle down and runn nicley , so i was asking if you leave the iar screw at the settings and set the idle screw on carb 2 that controlls all 3 then if needed ajust thurther the top and botton independantly to gain more idle out of one carb than another one

fast fred · 16 March 2007, 13:33

check it over for a vac' leak, don't see a lot of them over hear, thare is an idel speed screw, then thare are ( don't see many of them hear) most-likely,low speed mix screws,on the main body of each carb, start them at 1 1/2 turns out.

getit in water and fire it up, check for a vac' leak,turn the idel speed screw in till she holds at about 1000rpms, then adjust the mix of each carb, re set idle speed.

avon5.4 · 16 March 2007, 17:50

i know whot you mean about only one idle scew that controls all 3 carbs i will take off the other 2 idle screws then just adjust the one that controls all 3 , which should all be balanced , cheers for all info im going back to boat this weekend so will give it a try , my friend has noticed a noise on the drive shaft in the lag are there bearings in there and how hard are they to repair /get out

Nos4r2 · 16 March 2007, 18:24

Quote:

Originally Posted by avon5.4

i know whot you mean about only one idle scew that controls all 3 carbs i will take off the other 2 idle screws then just adjust the one that controls all 3 , which should all be balanced , cheers for all info im going back to boat this weekend so will give it a try , my friend has noticed a noise on the drive shaft in the lag are there bearings in there and how hard are they to repair /get out

Mate, ebay it and buy another engine. Bearings or not (I've never stripped a Selva) you're never going to trust it enough to use it now.

avon5.4 · 16 March 2007, 19:10

i shall see wot like this weekend then it will be put up for offers comlete if the engine does not stop messing with me