Johnson 6 hp carb issue?

[Hoppi84]

Had the motor out today and was only getting 2500 rpm at wot... itd rev higher in neutral and was able to get another 100 rpm before just calling it quits... gonna go check compression and spark in a few and will report back

 

[racerone]

Model # is ?

 

[Hoppi84]

6r74c

 

[Hoppi84]

The powerhead is at least a 71 I believe from the oil drain valve on intake

 

[Hoppi84]

Spark was jumping a 1/4" but compression seems low at 75 with a new head gasket

 

[racerone]

Any pictures of this oil drain valve ?

 

[Hoppi84]

Not of my actual motor but it 42 43 44 on parts diagram

 

[Hoppi84]

If my powerhead was a 68 and took a 49d high speed jet and it's running a 44 would that have any effect?? I have two high speed nozzles but ones fatter??

 

[Hoppi84]

It appears I have a carb from a 68ish with the plastic cam roller and a carb from a 65-67 with the round roller which was on it when I got it and both seem to be different high speed orifice but have two 44

 

[Tim Frank]

What is the running history since you owned it?
i.e. has this run OK for you previously or is this an unknown entity just acquired?

 

[Hoppi84]

Pretty much an unknown to me... I had it running in a barrel before pulling the power head to clean water passages cause it was overheating and swapped all gaskets... going by bracket the powerhead gasket set I got wasn't right cause my manifold has the oil drain valve.... the freeze plug was gone on block with rph so just trying to figure out the year...

 

[Hoppi84]

So the gasket on the intake were for a 74 from going by the bracket tag but after looking thru parts of different years the inner leaf plate gasket had a cut out for the oil drain valve which I added but also after diving deeper there's at least 5 other holes that I covered up... so gonna get new gaskets ordered up and possibly a new high speed orifice of 49d...

 

[Tim Frank]

If my powerhead was a 68 and took a 49d high speed jet and it's running a 44 would that have any effect?? I have two high speed nozzles but ones fatter??

Do not think a 44 vs 49 would give such a dramatic difference in performance as you are getting

The "D" just means it is a 1/4-20 thread to mate with the carb....there are also 49...that is a 8-32 thread and a "C" type which IS ALSO 1/4-20 thread but differs from "D". There is also a 5/16 thread series.
All have a #49......that is just the ID in thousandths of an inch.

 

[Hoppi84]

Probably not but maybe the jet or me using the wrong gasket on crankcase side of intake possibly??? I looked and from 68 til 71ish the jets were different is why I'm asking and one was nla so probably gonna stick with the 65-67 carb with roller since I found the jet so well see....