Zenoah not idling too well

[Muddy]

Hi All,

Been a while since I visited here.

I have a mates boat in my garage today, he says it hasn't been run for a year. I don't think he drained the fuel (bad man!)

It is a fibreglass Enforcer hull with a Zenoah (260 I think - not too sure, as I prefer nitros)

I noticed the choke was still on a small amount, I have made a new choke lever from an old servo horn (now I can turn the **** thing on and off)

I fired it up, tuned the high needle like a chainsaw (lean - peak revs, then richened off a bit to drop the peak revs down a bit) about 1.5 - 1.75 turns out.

Carb is a Walbro.

I now have the idle speed up a bit, just to see where the low needle is best.

It seems good at 1 - 1.5 turns out.

However, after doing this, and settling the idle speed back down, the engine will run very well on a burst of power, but allowing it to come down to idle it revs lower than how I've set it.

Have I just made high end a little too rich?

or is the carb needing disassembly?

It's as though it floods a little when the butterfly drops to idle/closed (open by 1 or 2 mm still.)

fuel is new, plug is a good browny grey. Spark is fat.

I know it's a fuel issue, but I'm running out of ideas.

Anyone???

 

[Don Ferrette]

Hi All,
Been a while since I visited here.

I have a mates boat in my garage today, he says it hasn't been run for a year. I don't think he drained the fuel (bad man!)

It is a fibreglass Enforcer hull with a Zenoah (260 I think - not too sure, as I prefer nitros)

I noticed the choke was still on a small amount, I have made a new choke lever from an old servo horn (now I can turn the **** thing on and off)

I fired it up, tuned the high needle like a chainsaw (lean - peak revs, then richened off a bit to drop the peak revs down a bit) about 1.5 - 1.75 turns out.

Carb is a Walbro.

I now have the idle speed up a bit, just to see where the low needle is best.

It seems good at 1 - 1.5 turns out.

However, after doing this, and settling the idle speed back down, the engine will run very well on a burst of power, but allowing it to come down to idle it revs lower than how I've set it.

Have I just made high end a little too rich?

or is the carb needing disassembly?

It's as though it floods a little when the butterfly drops to idle/closed (open by 1 or 2 mm still.)

fuel is new, plug is a good browny grey. Spark is fat.

I know it's a fuel issue, but I'm running out of ideas.

Anyone???

What model Walbro carb? The number is cast into the carb body & generally starts with WT- .

 

[Don Ferrette]

Hi All,
Been a while since I visited here.

I have a mates boat in my garage today, he says it hasn't been run for a year. I don't think he drained the fuel (bad man!)

It is a fibreglass Enforcer hull with a Zenoah (260 I think - not too sure, as I prefer nitros)

I noticed the choke was still on a small amount, I have made a new choke lever from an old servo horn (now I can turn the **** thing on and off)

I fired it up, tuned the high needle like a chainsaw (lean - peak revs, then richened off a bit to drop the peak revs down a bit) about 1.5 - 1.75 turns out.

Carb is a Walbro.

I now have the idle speed up a bit, just to see where the low needle is best.

It seems good at 1 - 1.5 turns out.

However, after doing this, and settling the idle speed back down, the engine will run very well on a burst of power, but allowing it to come down to idle it revs lower than how I've set it.

Have I just made high end a little too rich?

or is the carb needing disassembly?

It's as though it floods a little when the butterfly drops to idle/closed (open by 1 or 2 mm still.)

fuel is new, plug is a good browny grey. Spark is fat.

I know it's a fuel issue, but I'm running out of ideas.

Anyone???

What model Walbro carb? The number is cast into the carb body & generally starts with WT- .

 

[Muddy]

Thanks Don, for your help... i will get the No. of the carb to you tomorrow...

The bench test is far different to the "real world" of a boat IN THE WATER

I have a 1/4 scale drag car powered by a Poulan 44cc chainsaw motor, and I find myself drawing parallels to the tuning of this.

The pipe on this is the size of a Baseball Bat-

I also have had numerous Nitro on and off road cars for the last 10 years.

I am also a fully qualified Auto Electrician,(11 years), but gave the game away in 1994 to pursue a career in Industrial Automated Packaging Equipment...so you see, no dumb ass when it comes to technical challenges!

I just needed some feedback to be sure I was going in the right direction.

I will disassemble the carb (and get the number) tomorrow, and see if the screen is blocked with old fuel varnish,

and I will also check the needle and seat. Probably a dose of Clean-R-Carb or Contact Cleaner will help here.

The seals for the carb to Spacer to Engine are good. No air leaks will be present here. (Gaskets are all good, and all bolts are "torqued" up.)

thanks for the tips, mate!

Happy New Year to all!!!!!

 

[Don Ferrette]

Thanks Don, for your help... i will get the No. of the carb to you tomorrow... The bench test is far different to the "real world" of a boat IN THE WATER

I have a 1/4 scale drag car powered by a Poulan 44cc chainsaw motor, and I find myself drawing parallels to the tuning of this.

The pipe on this is the size of a Baseball Bat-

I also have had numerous Nitro on and off road cars for the last 10 years.

I am also a fully qualified Auto Electrician,(11 years), but gave the game away in 1994 to pursue a career in Industrial Automated Packaging Equipment...so you see, no dumb ass when it comes to technical challenges!

I just needed some feedback to be sure I was going in the right direction.

I will disassemble the carb (and get the number) tomorrow, and see if the screen is blocked with old fuel varnish,

and I will also check the needle and seat. Probably a dose of Clean-R-Carb or Contact Cleaner will help here.

The seals for the carb to Spacer to Engine are good. No air leaks will be present here. (Gaskets are all good, and all bolts are "torqued" up.)

thanks for the tips, mate!

Happy New Year to all!!!!!

The carb number is on the outside of the body & does not require disassembly. If you are going to service the carb you should replace the diaphrapm, they don't last all that long in the conditions we subject them to.

 

[moparbarn]

needle & seat and diaphragm-sounds right to me. plan on rebuilding the carb, the diaphragm is probably hardened from sitting. that won't allow the needle & seat to seal, running rich, particularly at idle. when you reassmeble the carb, test the needle & seat to a couple psi. not too much, you can "blow them open" with too much pressure. a little will tell. if it still won't seal, you can 'polish' the seat in the carb with cleansing powder (comet/ajax), a q-tip, and a variable speed drill. a little powder on the seat, 1/2 a q-tip in the drill, and light pressure at med. to low speed should clean it up. saved a ton of chain saw and weed wacker carbs this way, seat is usually part of the housing, not available by itself. try your local lawn mower or outdoor power equip. dealer for the kit/parts. the kits are somewhat generic, and will service more than one # carb.

 

[matt]

Hi All,
Been a while since I visited here.

I have a mates boat in my garage today, he says it hasn't been run for a year. I don't think he drained the fuel (bad man!)

It is a fibreglass Enforcer hull with a Zenoah (260 I think - not too sure, as I prefer nitros)

I noticed the choke was still on a small amount, I have made a new choke lever from an old servo horn (now I can turn the **** thing on and off)

I fired it up, tuned the high needle like a chainsaw (lean - peak revs, then richened off a bit to drop the peak revs down a bit) about 1.5 - 1.75 turns out.

Carb is a Walbro.

I now have the idle speed up a bit, just to see where the low needle is best.

It seems good at 1 - 1.5 turns out.

However, after doing this, and settling the idle speed back down, the engine will run very well on a burst of power, but allowing it to come down to idle it revs lower than how I've set it.

Have I just made high end a little too rich?

or is the carb needing disassembly?

It's as though it floods a little when the butterfly drops to idle/closed (open by 1 or 2 mm still.)

fuel is new, plug is a good browny grey. Spark is fat.

I know it's a fuel issue, but I'm running out of ideas.

Anyone???

Hey sounds like one of three things crud in the carb , warped intake (happens because Zenoah factory bolts are a bit to long holding the carb on) or a bad seal in pto end of engine. I'm sure it will be one of the first 2 .Is the pump and metering diaphram soft ? the metering side is the needle side if it is stiff it will hold the needle open and flood you out if the pump side is stiff you will never geta happy needle setting for the high or low . check the intake for flatness this is a very common problem

 

[Muddy]

Thanks, gang!

I found a layer of varnish on the needle & seat, that wiped off with a cotton bud and acetone. The carb spacer/insulator was OK, and the only dumb thing I have done is Idle is a bit slow! I'm used to a low idle, cos I mainly play with cars.

Anyhow, it runs OK now with a higher idle speed. Needless to say, my mate is happy!

 

[moparbarn]

cool!! good news is always nice .

 

[Harald1966]

Hi

I am no expert on this but "everybody" seems to replace the original carb with the 257 carb nowadays.

If i don't remember wrong, he carb you refer to often runs best if the high speed needle is around 1,00 to 1,50 turns out, and low speed needle is 2,50 to 2,75 turns out. But they all will respond differently.