minimum and ideal compression for GT 150

[bardern]

I am new to Johnson engines and I am wondering where the compression should be on a mid-eighties GT 150, ideally and minimum needed to run well. I am having hard staring problems and at times severe bogging trouble at speed.

What is the differance between this engine and a non GT 150? What is a loop charged motor?

Can anyone one out there help a converted Black Max????!!!!!

[ChampioNman]

Welcome to the site. First off you have a cross flow motor not a looper. Second I'd say anything over 80 would be sufficient. Third the GT has a 35 amp alternator and a little more oomph and a few more bells and whistles. Your model # would help greatly. should be J150STLXX where the XX are letters this tell the model year. CM

[Dhadley]

The XP/GT's had different heads. Pretty good ones actually for stock factory heads. And some of the XP/GT 150's had port timing very close to the 200's. Obviously there were styling differences too.

[bardern]

Thanks for the help guys here is some more info.

Model Number : J150STLCDC

Compression : Right 90-91-82 Left 91-94-87

Is there any chance that this is a timing problem? The carbs have been rebuilt, new CDI, seems to have good spark. Like I said earlier starts like a pig, and cuts out at any where from half to WOT

If the block can take an over bore is this model a good candidate for a performance rebuild? What can I expect from a .020" overbore, Wisco piston Boysen reeds, etc. Am I further off to replace with a newer engine. It is hung on the back of a restored 350V Ranger which I wouldlike to get at least 60 MPH out of.

[ChampioNman]

The comp numbers ar about normal on your motor and not out of whack at all. You won't notice a significant increase in comp by an overbore it is just to help the rings seal up. you can go up to .030/cyl. For me I don't like Wiseco's on a normal rebuild. But that's me, on a stock rebuild. Now if you are wanting to turn you motor in to a full blown race motor the go here http://www.screamnfly.com they'll tell you how to hop your motor up. No Hop ups here!!

[bardern]

I am not looking to modify the 150 to the ragged edge, I am looking to improve it overall. Being from the north country I have worked a lot on two stroke snowmobiles and am wondering if the same basic principles apply. Sleds are generally taken to the maxaimum, eg 175 hp from 1000 c.c's.

Am I correct in that the GT 150 is the basis for the 175 and 200 horse power OMC's? Is the differance carbs, timing, heads?

[DoferGofer]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bardern &raquo;</TD></TR><TR><TD CLASS="quote">
Compression : Right 90-91-82 Left 91-94-87
</TD></TR></TABLE>
Compression is good.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bardern &raquo;</TD></TR><TR><TD CLASS="quote">

Is there any chance that this is a timing problem? The carbs have been rebuilt, new CDI, seems to have good spark. Like I said earlier starts like a pig, and cuts out at any where from half to WOT
</TD></TR></TABLE>
First things first. Get a manual for your engine and read and take on one problem at a time.

Now, the cutting out and/or bogging could be many things timing, probably not but, should be checked.

Carbs should be cleaned & Lync/Sync set.
Check all electrical component Powerpacs, stator voltage regulator.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bardern &raquo;</TD></TR><TR><TD CLASS="quote">

If the block can take an over bore is this model a good candidate for a performance rebuild? What can I expect from a .020" overbore, Wisco piston Boysen reeds, etc. Am I further off to replace with a newer engine. It is hung on the back of a restored 350V Ranger which I wouldlike to get at least 60 MPH out of.
</TD></TR></TABLE>
Get your motor running as good in the best factory tune you can and then, if the performance is not satisfactory to you. Get a bigger motor.

Regards,



Modified by DoferGofer at 1:00 PM 7/16/2006