Robins revving/engine speed problem

[Pocono Country Boy]

Originally Posted by bajamanjc

Thanks Brew, I also heard that the mechanical fuel pump needs compression to work? Is that true, on cars they have an arm that works off the camshaft on some and crank on others.

True...it uses compression to function. (fluctuations in crankcase pressure to be exact)

[jbar]

Sorry to jump on your thread, but I have a very similar problem with my 79 Robin engine. It does not sound like my problem is as bad as yours, so if you do find a solution, based on the suggestions, please post what you find.

On mine, it takes about 5-7 seconds to get enough pickup up out of the engine to engage the clutch. It almost seems like the battery does not have enough juice to turn over the engine, then once it gets going, it is fine. Once the motor is running, I really don't have any problems. The cart has a lot of speed and some good power. The only problem I seem to have is a quick starting engine. I have been trying to eliminate some problem areas, I did replace the battery and the new one has a strong charge. Also, I had replaced the microswitch and solenoid. I believe both had intermittent faults, but I don't believe they were causing the slow starting. The new battery helps, but again did not fix the problem.

If you find anything that works or any other suggestions would be greatly appreciated. Thanks for everyone for all the tips.

[BrewCityMusic]

My 88 turns over really slow at first and then builds "turnover" RPM's until it starts - howeveronce it starts, it takes right off (mine I chalked up to wear on the starter, as all electrical has been replaced and none of that affected the slow turnover)

[bajamanjc]

Alright I have an update, Just did a compression test an the engine has 70psi and the plug had a good amount of gas on it. So I was thinking about the fuel pump not pumping fuel (was using an electric and worried about flooding) and took off the pump and the diaphram is not ripped or torn and looks to be in good shape. I heard a leaking fuel pump diaphram can lead to loss in compression.

Any suggestions before I pull the motor and check/change the cranks seal. Like I said earlier, previous owner honed the cylinder and bought rings. I installed the rings but I guess I could have flipped them in the wrong way?????? Any suggestions to get the compression over 100psi?

It did run with electric pump but took awhile to get going

[bajamanjc]

Well, I took apart the fuel pump and everything looked real good, next on the list is reseal the carb. Then try the crank seal with starter fluid.

Thanks

[bajamanjc]

Today I throughly cleaned the carb and took it completely apart, cleaned it with brake clean and reassembled it making sure it sealed perfectly (hi-tach and gaskets) to the elbow attaching it to the cylinder head. After resealing the carb and the fuel pump the compression was still 70-75psi. I sprayed starer fluid into the carb and it fired up real fast. Also, the stock fuel pump now works although I didn't measure the flow. Without starter fluid it took awhile or didn't start. I tried the flywheel side crank seal w/ starter fluid and no change.

However, I tried the clutch side crank seal with starter fluid and it cranked right up. So looks like that is next on the list.

Anyone know how much compression I could gain with a new crack seal???

[Dave Box]

You should have the throttle hard down when you measure compression to allow maximum airflow into the chamber. If your compression is still low some folks recommend spraying some oil into the spark plug hole. If the compression improves then the oil has formed a temporary seal on the rings. This is a useful test on a 4 cycle where you could be losing compression through the valves but to be frank the only realistic culprit on a 2 cycle is a worn bore.

Sadly the crankshaft seals will have no effect on your compression. You will also need to change them (and you really should do both at the same time). The job will be easier with the engine out so seals and a top end overhaul kit will have you up and running.

[bajamanjc]

Thanks Dave, I appreciate your help. I will check into a top end kit. I also thought about hooking back the electric fuel pump and hook up a tube to the carb hose and spray cab cleaner to prime the motor.

Off the subject though, where did you get your vinyl wrap for your cart...looks real nice!!!

[Dave Box]

I got the vinyl here
http://www.everythingcarts.com/c-79-...cID=&orderby=7
It was the cheapest price I could find and they are all made by 3M so the quality was great. In addition they are a forum sponsor and real nice people. If you enter code BG WILD they will give you a further 5% off.
BTW thanks for the compliment, it's always nice when other enthusiasts give you a shout out. I kept a blog of the restoration if you would like to see the before and afters click here.
All the best
Dave Box

[jasono]

yeah pump works off crankcase ventalation