Mower only warm starts with priming

[DaveyCrockett]

I wonder if anyone can help me with a perplexing problem.

I'm working on a Chinese mower Branded BMC Big 20 and it has an engine called Wolf 5.5 HP. Don't let that put you off it's a very standard OHV engine, with a very standard type of carb. It is pretty much the carb used on the Honda GCV160, but it is chokeless. It primes by pushing air into the top of the float chamber, and has very standard looking main and pilot jet arrangements. Everything is clean, armature gap set at 12 thou, compression was 80 psi, before I opened up the inlet valve clearance from 3 to 6 thou and the exhaust from 3 to 8 thou. I don't have any tune up specs on the engine so I'm just going by what I think should work. The engine is pretty new, probably ran for a couple of hours judging by the state of the mower.

It needs a lot of priming for cold start. It advises 5 or 6 pumps. It runs well once started, no hunting or spluttering, but it doesn't wan't to warm start without more priming one or two pumps. I have opened out the pilot jet just a tiny bit but that didn't seem to help. It has an adjusting screw for the pilot system so I knew I could bring it back if I overdid it. The butterfly is wide open on start so I guess it won't pull much fuel through the pilot jet anyway. I swapped the original main jet for one from a Keihin which I can afford to scrap and progressively opened it out until it is visibly larger but still it won't warm start.

I'm a self-taught mechanic and it's business death doing this much work on a customers machine but I would really like to understand how to sort this problem out for my own learning. If I carry on opening out the main jet, I presume eventually it will pull enough fuel to warm start without priming or have I missed something.

Many thanks for any advice on this. I know this kind of knowledge doesn't come easily, so I am very grateful.

 

[bertsmobile1]

You have an air leak on the priming system.
So either the bulb is leaking or the gasket behind the air box is leaking
Very common with the air prime system.
The plate warps particularly if the owner overtightens it.
A lot of times the air purge B & S engine need 2 gaskets to make up for the warping.

As for repairing cheap imported mowers that have no service logistics, I for one don't do it.

While we all enjoy a challenge, in the long run it is against the interest of mower repair shops to service disposable mowers.
If we keep them running they will dominate the market & we will all be out of a job.

When a shop brand comes in to me I always over quote substantially to cover the cost of faffing around trying to find parts that will fit.

Just sent a pressure washer back with a $ 400 bill for fixing an oil leak which ended up being because the hole in the crankcase was machined too big allowing the seal to spin in the case when the case got hot enough.
The engine was a GX200 knock off and just for interest I checked the fan against a real GX 200 one after I had worked out what was happening.
The copy was 20mm smaller in diameter had 5 less fins and was 10 mm shorter in height
the breather tube had crumbled away filling the sump with rubber fragments and the HT lead was cracked everywhere so when it got damp it shorted
The fuel tap on the carb broke off and a genuine Honda one had to be cut thinner to fit.
The fuel cap had fallen apart so the owner had siliconed it back together blocking off the vent.
The retaining bolt for the air filter cover had also broken away and the foam air filter did not make a seal against the air box.

The customer was told ( and they believed them ) the engine was made at the same factory that makes Honda engines and Honda parts would fit ( they don't )

The washer is 18 months old and had been used twice, but it was $ 700 cheaper than the real Honda one.

 

[DaveyCrockett]

You have an air leak on the priming system.
So either the bulb is leaking or the gasket behind the air box is leaking
Very common with the air prime system.
The plate warps particularly if the owner overtightens it.
A lot of times the air purge B & S engine need 2 gaskets to make up for the warping.

As for repairing cheap imported mowers that have no service logistics, I for one don't do it.

While we all enjoy a challenge, in the long run it is against the interest of mower repair shops to service disposable mowers.
If we keep them running they will dominate the market & we will all be out of a job.

When a shop brand comes in to me I always over quote substantially to cover the cost of faffing around trying to find parts that will fit.

Just sent a pressure washer back with a $ 400 bill for fixing an oil leak which ended up being because the hole in the crankcase was machined too big allowing the seal to spin in the case when the case got hot enough.
The engine was a GX200 knock off and just for interest I checked the fan against a real GX 200 one after I had worked out what was happening.
The copy was 20mm smaller in diameter had 5 less fins and was 10 mm shorter in height
the breather tube had crumbled away filling the sump with rubber fragments and the HT lead was cracked everywhere so when it got damp it shorted
The fuel tap on the carb broke off and a genuine Honda one had to be cut thinner to fit.
The fuel cap had fallen apart so the owner had siliconed it back together blocking off the vent.
The retaining bolt for the air filter cover had also broken away and the foam air filter did not make a seal against the air box.

The customer was told ( and they believed them ) the engine was made at the same factory that makes Honda engines and Honda parts would fit ( they don't )

The washer is 18 months old and had been used twice, but it was $ 700 cheaper than the real Honda one.

Thanks for the advice.

It has a connector on the carb for priming so it doesn't rely on gaskets to seal, but the primer hose is already in poor condition, and not easily replaceable with straight hose without kinking it. It's a pre-moulded hose which isn't easily obtainable. I did check out if a air leak was the problem by sealing off the priming connector but it still it doesn't warm start. I think I've ran out of patience now so it's going back to the customer as is.

I agree with your thoughts on the economics of repairing disposable equipment. It's my instinct to alway try to help people out and hate of waste but I usually regret it.

It would be good to see a law to stop the sale of equipment without a commitment to supply all the spares and manuals needed for repairs.

 

[bertsmobile1]

Funny enough we sort of have that here and I thought it was part of EU law.

The friendly sales man usually tells the customers "Honda parts will fit it " but generally they don't