I started my first port job the other day. I'm taking my time so I have less chance of making a mistake. I' about half done on my exhaust port. I plan on cutting mostly my exhaust and a little off my intake. Other than that I'm just cleaning everything up and shaving the head.

I'm working on a 96 300 Express. It's been bored (.040) with a Wiseco Pro Lite Piston and my carb has bored (.040). Air box has been modified and my exhaust.

Can anyone offer any tips or suggestions? I've got all the info I need from a friend of mine who builds race motors. He's got me pretty well set up but, I'm always willing to listen to any more info I can get.

 

How much are you cutting out of the exhuast? More is not always better. Do you know what the current timing duration value was and what your target is going to be.

What about the transfer duration. Cut the exh too high and dont do anything to the transfer and she turns into a peaky bit....yeah.

Any head mods in mind?

 

I didn't really plan on cutting up or down. Instead I'm going to double up my base gasket. This should give me about (.020). As for what I cut, all I did was widen my port. I widened it about (.250) total. I did end up taking about (.010) of the top and bottom just so I could clean it all up. I ended up by just tapering this back to the pipe side of the port. I'm only a couple of thousandths bigger there. Any other suggestions?

As for my transfer ports, I was told to basically leave them alone. I did have a couple of boogers at the corners of ports. I cleaned them up and knife edged the bottom of ports(at the base). Any other suggestions on these?

The intake is my last area of concern. I haven't done anything to it yet. My friend told me what to do to the exhaust and the transfer ports. He then told me about what happens when you do "this or that". He also told me about some basic theory's. He then some it all up with, "take a little of the intake." Followed by a big smile. This was meaning that I had to figure it out by myself. My friend knows I'm pretty smart and a bigger perfectionist than he is. So this was his way of challenging me. I know this because I used to do the same to him about other things. The problem is that I am nervous and I don't really want to trash a $400 jug. I do have a game plan but I'm not totally sure if it's what I want to do. Any suggestions?

As for the head, I'm going to wait until I bolt my jug back down and then I'll find out what my piston clearance is. Then I'll get my head shaved down to get my compression up to a good number.

I don't plan on racing this thing but, that is basically how I ride. I do also do some slower trail riding on occasion so I 'd still like it to atleast run under those situations. Mostly though I'm by myself and GETTIN IT! I'll pipe and carb it when I'm done porting it.

Once again, Any suggestions? Thanks!

 

2 of my friends have done there own porting, and now they are slower than they used to be last year. I will leave my porting to the pros...

RoostKing...

 

Well, I finished putting it together this weekend. Went for a 40 mile ride on Sunday to see how she would do. It turned out pretty well, I think. I used to be just slightly slower than this guy on a 300EX. Now I walk all over him off the line and all the way up to about 50mph before he starts catching back up. He will eventually pass me due to slightly taller top end, about 3 or 4 mph or so.

I wasn't satisfied with my compression though, when I was done. I decided to have it shaved a little more yesterday. Came home, put it on and still has the same compression(125#). I cut .040" off the first time and about .035" the second time. After my first cut I had .070" head clearance. Then before I took it to get shaved yesterday, I measured it again and it was at .090" clearance. I can't figure out how I gained .020" clearance for no reason. I used solder each time to measure it and have saved all the pieces I've used so I would have a reference later. The pieces say the same thing I am. I always take two readings everytime I check something just to be sure. Anyways, I'm down to .065" clearance now, when I started from .110".

The only other thing I can't figure out yet, is that after I put it back together yesterday, my idle jumped up a little. It isn't much but no matter what i do, I can't get it to come down any. Could this be because of the higher compression I've got. I haven't really checked it out yet, but I can't make any sence of what it could be for sure.

All in all this thing pulls really hard now it my mid range. It actually hits its hardest right at my shift point(remember, it's belt drive). I can roost gravel or loss dirt up to about 30mph or so before it will quit spinning and I run 25x13 Wolly Buggers. I'm going to have to do some more clutch mods and, carb and pipe it to see just how much I can get out of the old girl. It is still stock as far as the carb and pipe go.

I'll have to get a hold of another comp. tester to make sure I'm still only pulling 125# compression. I started out at 105# before the port job. It went to 125# after the port and head job. So, I shaved another .035" off the head and I'm still at 125# compression? I hope it's just my tester thats bad.

Overall though, my first port job was a big success. I'm glad I did it.

 

Are you working with a fresh piston and bore....if not you're in trouble...

IF you have worn components and you use that as your baseline to establish your cranking compression, then you start whacking away to get your compression up to your desired target. Sure that works fine. UNTIL...you go to put in fresh stuff and you have decreased the trapped volume SOOO much from before to get the compression up on the worn components, the new components will then send your compression to somewhere near the moon...DETONATION CITY!!!

You high idle could be from a lean pilot circuit or an air leak...

 

What Backcountry said about the worn components may also explain why your compression did not go up after additional milling of the head. Maybe 125 psi is the most it will hold without leaking by. Are you checking for air leaks after installing the head? Maybe your head is not sealing right anymore.

I don't know what is normal for your machine, but 105 seems pretty low. My FL350 stock was 138 and is at 170 psi after lowering the head a total of .043" giving me .070" clearance. That is .035" removed by only using one layer of three from the stock head gasket and .008" shaved from the head. .008" is the most I can just "shave". That is how thick the lip was before the squish band starts. If you cut into the squish band, you have to rechamber the head.

 

Generally speaking in a general manner, generally for each TEN thou removed from either then deck hgt, head gasket, or head, generally equals 10 PSI of cranking pressure.

Meaning you mill off .040 from the head, that would be about a gain in 40 psi cranking pressure....

 

My motor was rebuilt in April. It still looked like it did when I put it together then. I've put about 50 to 75 hours on it since then. My compression on this fresh rebuild at the time was only 115#.

The thing that seems weird to me about my high idle is that it didn't do it the first time I put it together. This idle problem only appeared after I had the head shaved a second time. Now if according to my tester, I didn't raise the compression any, why would this affect my idle? Which by the way I fixed by screwing my Air Idle screw in almost all the way. I'll have to jump up a size on my jet. I must say though, that my engine doesn't rev as quick off an idle as it did before. I'm going to have to find a happy medium. I unerstand about lean and rich conditions but I'm not sure how they very just by raising compression?

I also tried my comp. tester on my car and could only pull a high reading of 125# also. This really leads me to think my tester may be defective. I still haven't found another to try yet, but I will.

 

I bought a nice compression tester at oreilly auto parts. It has different fittings that thread into different cylinder holes. It only runs about 20 bucks and works really well. You might check it out.