Thread: General Carb running Rich - killing spark plugs

I’m not familiar with this carby but suspect some of the jets may be an air blead so if blocked will cause a richer mixture.
I’d also double check the coil is corect(ballast or non-ballast)

G'day All,

Maybe the accelerator pump diaphragm is leaking. Can you see if the vacuum is sucking fuel from the discharge pipe all the time?
Chris

Originally Posted by alien

I’m not familiar with this carby but suspect some of the jets may be an air blead so if blocked will cause a richer mixture.
I’d also double check the coil is corect(ballast or non-ballast)

I am not sure if there is an airbleed system but if anything is blocked I will check it on dissambly.
It has the correct coil - the same brand and model since I have had it.

Originally Posted by Busted Syncro

Can you see if the vacuum is sucking fuel from the discharge pipe all the time?
Chris

Hi Chris not sure I follow - are you meaning to look in the carb and see if fuel is dribbling into the intake all the time?

Thanks to both of you for the comments - very helpful.


Garry

G'day Garry,

Yes look down the carb throat at idle and see if fuel is being sucked out of the accelerator pump injection tube. Not familiar with that Zenith however, common fault with the Solex.

Just a thought!
Chris

Hi Garry,

Been going through soul searching ignition issues, but with a 350 on lpg.

First thing I'd say is the '7' is the heat range in your NGK plugs, not sure why you're using them.

I have been running the same plugs that came with my POS for years..... NGK BP6FS but did check with the Chev guru in Geelong 2 days ago and he just said 'that's right,5 is the heat range for petrol, 6 (colder) is right for lpg'.

I'd suggest '7' is way too cold for petrol.

Gone a bit further with the ignition, have done the research, and am getting rid of the points, condenser, etc and going with a FAST XR3000 optical system with a PS 60 coil.

Probably will put it in tomorrow.

In addition, I'd say that a split accel. pump diaphragm can do as others have described, from personal experience with a 302W.

DL

Hi Garry,
I am a motorcycle mechanic .What I am finding is motors that have been tuned 5 - 10 years ago have to be leaned off by about 10% to get the same performance out of them. You are best to use a BP6HS or if you want to stay with the 7 heat range then go BP7HS.
BP is extended nose. Never run 98 octane in a carbie road motor as it will always run rich down low. I do not know what sort of valve seats are in your motor, but most old motors need hard seats to suit unleaded petrol. Paul.

Originally Posted by 350RRC

First thing I'd say is the '7' is the heat range in your NGK plugs, not sure why you're using them....... 5 is the heat range for petrol, 6 (colder) is right for lpg'.

I'd suggest '7' is way too cold for petrol.

Gone a bit further with the ignition, have done the research, and am getting rid of the points, condenser, etc

In addition, I'd say that a split accel. pump diaphragm can do as others have described, from personal experience with a 302W.

DL

Thanks for the information - great stuff.

The NGK B7HS plugs were in it. and I have just continued to use them. The specificed plugs for the vehicle are Bosch W225T1 and I just cross referenced them and the NGK B7HS are a straight cross match. So are the correct plug for the engine.

Other direct matches are
Champion H8C
Champion L82C
Champion L82CT10
NGK 2792
NGK 5110

Of all these the NGK B7HS are easiest to get. These are only about $15 a pair so I guess I can try the same in the 5 heat range and see what happens.

I originally had a pertronix electronic ignition system in it but when I started having troubles I took it out and went back to points using new components in case part of the problem was the electronic module. When I finally sort all this I will put the petronix back in.

I agree about the accelerator pump - and will soecifically check it when I pull the carb apart - I have new bits.

Thanks for your input.

Garry

Originally Posted by powerband

Hi Garry,
I am a motorcycle mechanic .What I am finding is motors that have been tuned 5 - 10 years ago have to be leaned off by about 10% to get the same performance out of them. You are best to use a BP6HS or if you want to stay with the 7 heat range then go BP7HS.
BP is extended nose. Never run 98 octane in a carbie road motor as it will always run rich down low. I do not know what sort of valve seats are in your motor, but most old motors need hard seats to suit unleaded petrol. Paul.

Thanks for your comments - see my comments above about the spark plugs. The only reason I am with the 7 heat range is because of the specified plug is in that heat range - I accept maybe trying a 5 or 6 may be better.

My engine is basically half a VW engine and similar to older motorcycle boxer engines. The heads are all aluminium so have iron based valve seats but as a precaution I also put in FlashLube Valve saver with each fuel fill. I normally run 95 octane as I have a higher compression ratio but it is OK on 91 octane - Standard timing is about 7 BTDC and the system has no vacuum advance.

So will a 5 or 6 heat range held burn the soot a bit better - the reason I ask is that even when it ran well it was always a bit rich which at the time I put down to the altitude being at 650m so a little less air than at sea level and maybe a bit richer running as the carb has fixed jets with no altitude adjustment.

Cheers

Garry

Thanks