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Can't find the numbers anywhere. Just rebuilt mine and did compression check....about 98 lbs per cylinder. Battery wasn't fully charged, but this seems low. Both were same.
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Re: 640 Compression?
The battery NEEDS to be fully charged, and you NEED to know if your gauge is accurate or not. You should be 150.SBT Tech Support is here to help with your problems.
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Re: 640 Compression?
I would run it a time or two (Break in procedure) just to get a feel how it runs and re-check it with a full battery and the engine slightly warm. It will probably go up to 105-110. Everyone says it should be 140-150 but I have two 95 Daytonas and both register around 110 but both run like Scalded Dogs (one has an SBT engine I put in it last November). I've checked them with different compression gauges (at least 3 different ones) and always get the same reading (around 110). It was totally mind boggling but I finally gave up trying to understand. As long as they keep running like they do, that is all that matters to me.Comment
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Re: 640 Compression?
Shark, Thx for response. I feel better with the compression reading at 115 on both cylinders after rebuild. Idles nicely on trailer. Only thing that concerns me right now is the fact that I can't get the thing started without putting gas or starting fluid down carb. Switched the carb from my other twin jetski and it won't start with it either. I pressure checked engine and all was good. Gonna rebuild carb and hope for improvement. Started right up before the rebuild. Any ideas?Comment
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Re: 640 Compression?
There is a fuel line that runs out of the fuel pump on the front side of the Mag Side Carb. Pull it loose and hit the starter for a few seconds and see if fuel is pumping out of that line. If so then its probably the carbs, if not then probably the pump diaphram. Either way, rebuild them because the kits also come with fuel pump gaskets but that just lets you know the pump is pumping.Comment
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Re: 640 Compression?
Nice tip.....should have thought of that myself. Rebuilt carbs on both skis today. Seems to run good at idle on trailer. Will test soon. I just did a compression check on my other tigershark Montego (have twin skis). It has 145# compression and has never been rebuilt. The one that I just rebuilt has 120....wonder why? Is there different compression for the 650 (644cc) engine compared to the 640 (639cc) engine? I know that the 640 has a higher compression ratio. Maybe the other engine is a 639cc.Comment
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