1965 merc 110 backfires at 7 to 8 mph

[Fisnfool]

I have a 1965 18' Starcraft Holiday that had the engine machined and valve seat hardened in 2005. ( per service paperwork given to my by original owner)

It is a 4 cyl inline.

As the throttle is advanced, between 7 & 8 mph the engine backfires once or twice then accelerates. and can go to wot without any other problem.

Below 7 & 8 mph engine is OK.

Any ideas on the cause? I looked at the distributer and did not see a vac line on it. Does it have only a centrifugal advance?

Any ideas why the backfire would be only as throttle is advance through the above speed or if held at that speed?

Thanks to all that reply.

 

[Fishermark]

Re: 1965 merc 110 backfires at 7 to 8 mph

I don't really have a specific answer, but some simple things to check:

1. Point dwell. In fact - maybe a tune up is in order including points, condenser, cap, etc.

2. Check to see if your accelerator pump is working - does it shoot a good stream into your carb at acceleration?

3. Yes, you have a mechanical / centrifugal advance. Check the condition of the springs and weights under the points plate in the distributor.

 

[jerryjerry05]

Re: 1965 merc 110 backfires at 7 to 8 mph

Check the things Fishermark said then check for water in the fuel???? Jerry

 

[chiefalen]

Re: 1965 merc 110 backfires at 7 to 8 mph

Whats compression on that real ole girl? Please, please, please, don't run it at wot for more than a few minutes. Try to stay 500-600 rpm under wot.

Carb clean? Filters are all clean?

Fuel water seporater installed on that boat?

Whats the spark plugs look like?

Good luck!

 

[Fisnfool]

Re: 1965 merc 110 backfires at 7 to 8 mph

Thanks for the replies.

I printed them and will post results later.

WOT is not used. I have a bad back and can't take the jolts on Lake Erie.

Mid throttle is my preferred max.