Jetdriver69

First itme posting with an engine question. I mounted a Zenoah 320PUM to a 3D printed 70mm jet drive in a scratch built kid sized 6.5 ft speedboat I made for my grandson.
The engine is brand new and never ran, but I cannot get it to fire.
I've checked the spark plug for decent spark and it is getting fuel for sure. The spark plug does smell of fuel but not overly wet. Regapped the plug for .065 mm just to make sure and using Klotz oil and 95 octane gas, so that shouldnt be the issue.
I even completely disconnected the kill switch in case that was the problem.
Ive tried the press the primer twice then cover the velocity stack with my hand and slowly pull the engine over twice. Then choke and pull multiple times. But again no start.
I've tried starting fluid with no luck. I've tried pulling at idle, 1/3 throttle, 1/2 throttle and full throttle with no luck.
Could the carb settings be out of whack? Maybe the gap spacing on the coil needs regapped? The spark looks strong in the dark but could the compression be so high that the spark isnt strong enough to light off inside the cylinder?
Should I try to start it with the exhaust off? Im about to rip everything out of the engine bay and bench mount the engine to see what the heck is the problem.
Thanks for any suggestions.

dwr9

I assume you mean you set the spark plug gap to .65mm not 065mm. It sounds like you have a carb with a primer bulb. if so press the bulb until you are sure there is gas in the carb. If enough gas has reached the carb you shouldn't really need to choke the engine to start it. Do you know what carb is on the engine? Where do you have the needles set? Doug

Jetdriver69

Yes .65mm. Yes it has the primer bulb, I think it is a 1048 carb. The needles have not been touched, so whatever they came from the factory.

Should I start at zero with both needles are try reset? Which way to turn and how many turns to get to the null setting on the hi and lo needles?

Yes there is plenty of gas getting to the engine, primer bulb is full. Maybe Im just constantly flooding the engine using the the choke.

The plug smells of gas but very little fuel comes out the plug hole if I pull it over without the plug installed.

I am assuming if I see spark at night with the plug out grounded to the head, then the coil gaps are ok. Maybe the plug is weak and the spark isnt hot enough?

I really want to exhaust every possibility before I rip the engine and exhaust out and bench test it.

I tried to post pictures but dont have enough posts yet to allow it.

Thanks!

dwr9

I don't think your carb is a 1048. The 1048 does not have a primer bulb. From what I see online it may be an 1107 and I don't know what the needle settings should be on that carb. According to the G320PUM manual it says 1 7/8 on the H and 1 3/8 on the L. To set you turn the needles in as far as they will go, but don't go too tight or you could damage the needles or seats, just until they are lightly closed. turn them out to the settings suggested by the manual and it should run. They may need some fine tuning when you actually run the boat. Doug

Jetdriver69

Yeah it is a 1107, my bad.

I talked with the RC boat guy who sold me the engine from Zenoah.

He said to prime until the bulb is full, then pull through once with your hand over the velocity stack. Twice will most likely flood it.

Then choke and set 1/2 throttle and pull away. Maybe shoot some starter fliud down the stack.

If I flood it then pop out the plug and shoot compressed air into the cylinder to clear any fuel as I can't turn the boat upside down.

it is 6.5 ft long and weights at least 80 lbs without ballast.

I'm still going to null out the hi/lo needles and reset to factory specs in case they are out of whack before trying the new technique.

Could the engine being directly connected to the jet drive without any clutch cause it to drag during the engine pull and maybe not spin up fast enough to start?

This is getting frustrating.

Jetdriver69

Ok got the 320PUM started and it starts consistently now.

No choke, very little prime, one slow pull though and a tiny shot of starting fluid and it kicks off with 3-4 pulls.

That little 32cc motor has got some balls for sure, I believe it does put out 4.3 hp at peak rpm

Even at idle and directly connected to the jet drive, it is putting out enough thrust to push the boat around with a kid on board.

At 1/2 throttle the boat pushed me over in the pool as I had wedged the bow agaisnt my chest and working the throttle.

Going to have to install some kind of idle stop on the throttle until the kid gets a bit bigger as I'm sure the boat may do 10-15 mph or more at high rpm.

When I have enough posts I will post pictures.