Calling all 170 owners with a 70/100 hp motor....

[Georgie]

PSC -

Still with ya.  Have been in the field for work all week.  No computer time.

I'm a bit scattered trying to provide info for both the 70 and the 100 in one thread.  Perhaps dedicate this thread to the 70 HP since it's in the thread title, and start another for tuning the 100?  I imagine you'll get more poignant and specific responses.  Your jets do appear to be factory original.  Need description/photos of spark plugs for each cylinder still.  Also, have you been able to speak to any local shops about testing propellers? I'm curious what a slightly steeper pitch prop might do for your ride.  The more info you provide, the more people will respond, and while a pain to provide, pics really do encourage others to reply.  

Your javelin, does it have the stock "bubbleback" exhaust between the cylinder heads?

Your carbs, what size throat is stamped in the forward face of the aluminum?

[fitz73222]

Hey Guys,
I've been watching Georgie maneuver through the details on this with some outstanding information. I just want to make a couple of points. First, all 2 stroke engines have loose pistons when cold. The tightest clearance is in the skirt area below the wrist pin. The skirt is what keeps the piston running square and parallel to the bore. Thats why you will usually see minor scoring show up on the bottom of the piston first. When the engine warms up, the piston will expand to a running clearance of .001-.0015 and the oil film is what keeps the bore and skirt happily almost rubbing against one another and protects the two from coming in physical contact. the upper part of the piston has more clearance and the rings support the piston and are allowed to breathe back and forth (in and out) for compression and exhaust strokes. This breathing is what keeps the ring lands on the piston clean and not jamb with carbon from combustion. Again, the only thing preventing physical contact is a very thin film of oil.  OMC called the rings "pressure back" because of their design and the self-cleaning action. As for our V4 fuel economy, I would definately check full advance timing and see if its anywhere near where it is supposed to be. Then go through a meticulous throttle and timing syncronization process exactly per a factory manual. When we did Scotty's 75's on Miss Delmarva, the engines were so far out of time and throttle sync that I cannot understand how they even ran. Some people feel compelled to just start turning screws without any knowledge of what they're doing. My $1.385

[powersportcomposites]

I suppose I should have said this in my last post. I have decided the 70 isnt ever going on the 17. I may fix it and sell it but for our current purposes, disregard the 70 entirely. In light of this would it be appropriate to start yet another thread? I just didnt want to ticdk anyone off by cluttering up the forum. And once again thanks so much for all input so far. Georgie I will provide the info requested in a few hours

[Capt. Bob]

How bout you change the section of title of this thread from "70hp" to "100hp".
That way, you can continue the thread.

Work for you?

Thanks.

[powersportcomposites]

Can I do that? I dont see an edit option

[Georgie]

PSC-

Saw your fuel tank thread and it reminded me to get back to helping dial in your Javelin.  Carbs do not appear to be your immediate problem, so we'll need a few answers to some additional questions to keep going.

1) How do your spark plug electrodes and insulators look?  Black and sooty or oily?  brown/coffee colored? white and ashy?  can you send photos, and do all 4 plugs look the same, or is there variation top to bottom or side to side?

2) Do you have a timing light and/or know how to test timing?  Fitz has a VERY good point that the timing could be off.  If it's retarded or advanced you'll get sub-optimal combustion which means less power to push the boat, poor fuel efficiency, and can even damage the engine in a relatively short amount of time.

3) Still would like info on the RPM's when at WOT, especially the numbers you see using the two different props.  RPM's at idle would also be helpful.

4) What's the carb mouth measurement (stamped on the face of the carb)?

[powersportcomposites]

The plugs were VERY brown and oily. Looks super rich to me. I'll post pics tonight. They were all equally brown and oily. I do in fact have a timing light.