Upgrades for 720's

[seadoobie]

I was planning of refreshing my 720's over this next fall/winter. I really dont know how many hours these engines have on them since 1999...I'm trying to stick to the rule "If its not broke..dont fix it"...but these engines could have alot of wear on them. The previous owner didnt know much about it when he bought it form a dealership used. He owned it about 4 years with no real problems according to him...and it does run great.

I guess what I want to know here is what are good hp upgrades I can look into buying for these engines without really compromising reliability, so I can get a budget togeather. I was hoping there was a stroker kit out there but it looks to be alot of trouble & the info on a sleeper kit looks way out dated. Any input welcome!

 

[Dr Honda]

There are a lot of things you can do... but in a boat, it may not be worth it. I would recommend sticking to the basics. You can bump the compression a little, for a better acceleration, or you can install a better tuned pipe. Factory Pipe can get you 20 hp out of each of the 720's in your boat.

Personally... I wouldn't mess with it too much. You can spend a bunch of $$$ on the performance parts, and in turn, you may get 2 or 3 mph more up top. Also... if you don't know how many hours are on the engines, you may just kill them.

THe best way to check the condition of your engines is a quick compression test. 150 psi is perfect, and anything over 135 will be OK. Less than that, you are on short time.

 

[seadoobie]

they can run up to 6200-6800rpms for sustained periods of time with no problem...one side seems weaker than the other though in idle (neutral)..but that could be the drives...there not in the greatest of shape atm. So keep it stock is what your saying then....I can live with that!

 

[Dr Honda]

RPM's are irrelevant. If the boat is new to you... knowing the compression can save you a lot of $$$. When your compression starts to drop... the combustion blow-by is overheating the pistons, and the lower half. It is also displacing the needed oil. If your engines run well... but you compression is down to 132 psi... you can replace the rings ($15 + a gasket kit) and your engine may live for 4 or 5 more years. But, if you don't catch it... that engine may not live out the summer.

You can get a basic compression tool for $20 or less, and I feel it's a mandatory tool for a 2-stroke. I check the compression in my toys at least twice a year. It take's almost no time to do, and will tell you a lot about your engines.

 

[parrothd]

Factory pipes give wicked power, but you'll spend more time tuning and rebuilding your engines from lean seizure, I've had them on both my skis, and reverted one back to stock and the other is about to be converted. Just not worth the time and money, I'd rather be on the water than messing with it. The best thing you can do is call Dave @ impros and get new props and stick with stock setup...

 

[parrothd]

You can take that boat to the dealer and they should be able to tell you how many hours are on it via the MPEM.

I wouldn't worry about compression until it's really low, but do check the compression often so you can track any changes. When you rebuild the top end replace the crank so you'll have a completely new engine. I wouldn't cheap out and only replace the top end on a 10+ year old crank only to have it come apart and then you're have to rebuild the top end a second time. Do it right the first time, saves you money and time in the long run..

 

[seadoobie]

I think I'll go ahead & do a compression check when the weather clears up again & see where there at. I was thinking of sending them in to have them rebuilt when the time comes, have them balanced & blueprinted during the rebuild. So whos a reputable company to send them too?

 

[parrothd]

I've only used SBT and hot rod cranks, I think you're getting way ahead of yourself, you should probably use the boat before worrying about possible future work... My 98 1800 challenger has the original engines, these engines just don't wear out if you take care of them. Usually there's a ignored maintance issues with the carbs or oiling system causing engine failure, not from old age/usage..

 

[seadoobie]

So I'm going through everthing I can to make sure its solid. Aside replacing the impellers...everthing looks in good order atm. I'll try & find a decent compression tester & see where there at.

 

[seadoobie]

Ok so I finnaly got the compression test done today. They all came in at around 140 psi (+/- 3 psi)...this was tested on a brand new compression gauge. Its been setting for weeks now...and after the test they fired right up, no problem. So are these decent numbers?

 

[parrothd]

Yep, I recheck mine everyone once in a while or when I suspect something is wrong...

 

[drtyhatch]

so If someone was to install "factory Pipes" what kind of problems arise and what are the solutions? If they run leaner wouldn't the solution be to run a colder plug? I have no idea, thats why I'm asking these questions. I too have twin 720's and would like to know what can be done to get a little extra power out of them.

 

[Dr Honda]

so If someone was to install "factory Pipes" what kind of problems arise and what are the solutions? If they run leaner wouldn't the solution be to run a colder plug?

NO!!!!!!!!!!!!!!!


You would need to richen the jetting for the carbs. If you buy pipes... they will tell you what jets are needed.

 

[Dr Honda]

Double post.

 

[drtyhatch]

NO!!!!!!!!!!!!!!!


You would need to richen the jetting for the carbs. If you buy pipes... they will tell you what jets are needed.

ok, thats good info. thanks