1971 750 needs help- Compression Tight

hey guys,
I've been a lurker for a few years now and used quit a bit of the great information to help me with my bikes. I have a 74 850 and I was recently fortunate to find a 71' that has been garage stored for the past 30 years.

I have gone through the regular mantainence items, i've flushed the fluids and refilled, cleaned out the tank, cleaned the petcocks and put on new filters. Removed the floats from the carbs and cleaned.

When trying to kick it over the compression is extremely tight. When i take out the spark plugs it kicks pretty easily. I've tried a few tricks: flushing some carb cleaner into the sparks and even tried a few down the hill 2nd gear jumps. All to no avail.

Dont want to get in to deep prior to reaching out to get your guys thoughts on any idea's of what it could be. Any help would be greatly appreciated.

thanks
Paul

Well, there are 3 things to start it, compression, fuel, and spark. One of them must be missing or not there at the correct time. Check your spark, can you flood the carbs with the tickler? Have you checked the timing? Sounds like you need to do a complete tune-up to make sure all is in order. You can't guess at these things, they need to be in the correct order or nothing will happen. The carbs may need cleaning too.

Dave
69S

When you say the "compression is tight" do you mean that it is hard to get the piston to come thru the top of the stroke? You might take the valve covers off and rotate the engine through enough times to make sure the valves are all working correctly. Put it in forth gear and rotate the back wheel and watch. What happens when you try to compression start? Does it turn over or does it skid to a stop?

Russ

Paul

>>When i take out the spark plugs it kicks pretty easily.<<

Sounds like there is nothing internal stopping you from kicking it over other than its compression.

Try getting the kicker to the 9-10 o'clock position bringing it to compression.
When the pressure starts to drop off put all your weight on the kicker and bring it down with authority.
This is a pretty big engine and it doesn't kick like a 250.
If you can get it on the center stand you can focus on the kick and not worry about balancing the bike at the same time.
Don't put too much weight on side stand while kicking. It may fail.

Bob

thanks guys for the tips.

I'll take a look at the timing, spark and try removing the valve covers and see if they are working thru. I removed the front and they look to be moving ok, is it ok to put some oil in them to help get it flowing through. I had a thought last night to also check if the oil is flowing through from the oil tank, thought it could be tight as for its not properly flowing through to the pistons.

I've tried the kick as hard as i can technique but think i have to get in a bit deeper.

thanks for your help and quick responses, i'll keep you posted as i continue to investigate.

Its a '71 750, so maybe check the stamping on the head, above the right exhaust rocker cover. if its is "C" then its a Combat motor with 10:1 compression. The pre-850's had a short poor leverage kick lever which makes the kick over a bit tough. Replacing the lever with a Mk3 makes it bit easier.

Mick

Paul,
If it has decided it is not going to start for some reason, they can be very hard to push over. It's like hitting a brick wall. However, if they are willing to start, it gets much easier because the firing gas helps push you through each compression stroke and when it does start, you will be wondering what was so hard about it. You need to make sure it is not too advanced or it gets real hard to start. That's why the points are good, they start out near TDC firing at low rpm. Some of the electronic units advance the low speed too much and then you get hard starting and kickbacks especially with a low battery. Like everyone says, don't take any prisoners when pushing, I stand on the left peg with my weight all the way up, get the pistons just to TDC and give it the old one, two using my weight to get it through the second compression stroke.

If you are worried about the oil delivery, take off the primary, get a 1" spade bit (for wood) get a 3/4 drive 15/16" 6 point socket (Tractor supply has them cheap) and a heavy drill. Put the spade bit into the 3/4 drive, it fits just right, put the socket on the rotor nut, put the drill in reverse, take the plugs out, disconnect the battery, ignition off and drill away until you see oil coming out of the rockers and dribbling back into the tank. You won't get much pressure, but it will go through if everything is working. I used a Milwaukee 1/2" HD drill and it warmed it up pretty good, I had to let it cool off a few times before I got oil coming through, maybe 15-20 minutes total from an empty sump, rebuild engine.

Dave
69S

Thanks guys for the tips, to give you an update, i think the compression is just tight as for it needs to get some lube running thru once it starts.

I think I boiled it down to the points (but don't know how to fix them and one of the screws doesn't free up with the flat head screwdriver I have, needs a biggg head).  I did a test today to see if the plugs were sparking and the left did but the right didn't.  Changed the right 6v coil and now can get a spark but its intermittent.  I think I have to open up the points and adjust or replace the contact breaker (have an extra pair).

Hopefully that will get me the right spark, get some fluid running thru and see where I'm at.

Thanks  

ludwig, are you saying it is bad because the rpm is not high enough to build up enough oil pressure and thus not enough lube for the cam, even if the sump is full?

Dave
69s