Vmax4 squish

Woody255

Woody255

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Jan 5, 2016
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NW Ontario
Hi folks,

I'm looking for opinions here....What is a safe and acceptable minimum squish clearance on a Vmax4 800 race engine? Keeping in mind that high quality race fuel is used. This is NOT a trail setup. Thanks. Woody
 

woody, what ya have to figure out here is what your compression ratio is first. now just a fyi stock 800 was .068/.072 stock squish. 3;16x (yammie tony)
 
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It's a bit of a long story on this motor. Last year I built the motor with parts I had from my collection. They were 8BU cylinders with Hauck's porting, heads cut .025, Bender quads, stock carbs. It ran well, but since it's a dedicated snow drag rig, I wanted to take it to the next level.

Over this past summer, the carbs were bored by Gerry @ Bender Racing Canada (Great to deal with btw). New heads were also cut and re-domed by Gerry. I then sent my cylinders over to Justin Fuller to be re-ported to to match the new Hauck Howlers. It's been a lot of work getting it set up since I am basically starting from scratch......

My biggest issue was I always had a bog from engagement to 6-7000rpm. This bog was increased with all the new modifications. No matter what clutching combinations I tried, I couldn't lose the bog.

After numerous conversations and lots of advice from Justin, I measured my belt air gap on the primary at nearly .040" I have just replaced the split collars to a set .020" narrower. I will try it this week.

I am open to any suggestions on this project! Thanks.

Woody
 
let me ask ya, why would you post here about squish if you worked with gerry and justin ? gerry should have them set for your motor., just wondering. anyways ever think that bog could be in carburetion ? and sure clutching. 3:16x (yammie tony)
 
Because I had a few options to choose from for heads to use on this project. I was putting this together at a time when I could not reach these guys on the phone for suggestions, so I posted it here seeking advice. Gerry did these heads prior to Justin working on the cylinders. They were done at different times, by different people as my plans changed during the build. I was concerned that the squish I had may be too tight. I was trying to keep it "safe" as I have never taken a motor this far before.

I have played with the jetting, so far without success.
 
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got ya , very good answer woody. like i posted, you can run that squish pretty tight with the compression ratio and fuel you will need to use. two things are causeng that bog, either clutching or carbs. like you posted. 3:16x (yammie tony)
 
Thanks again. I beleive the reeds are stock cages, with Boyesan? carbon fibre pedals. I have inspected them closely, and they looks fine. I appreciate the feedback here. It's been a tough go getting this thing to run properly....Justin and Gerry have been excellent to deal with and I would recommend their services to anyone. At times they can be tough to reach on the phone, but they are very busy this time of year!
 
i had a problem with my 95 800 stocker doing sorta what your describing, and i have nothing like this sled here , i ended up changing pilots and replacing o rings under needle and seats. 3:16x (yammie tony)
 
Go through the carbs like Tony said.
If it's still a problem, Id swap your bored carbs for known good stock ones, retest.
Still issues, swap reeds for stock ones.

All the plugs have same good color? One isnt darker or off color?
 
woody i am sure you know there is basically only one belt to use on any vmax 4 , the 8bu-00 yamaha belt. i am sure you have checked sheave / clutch spider spec. 3:16x (yammie tony)
 
I'm out of my league here as I don't race but seeing as the problem has always been there just gotten worse with changes I'd be looking at things that haven't been changed and/or procedure with build/pre-race.

My .02 for what it's worth.

I interpret the word "bog" as an engine running issue not a clutching issue so I'm with Tony on carburation.

Now I know you've played with jetting to no avail but those stock carbs were set to run with air boxes. Running without them not only changes air flow through the venturi but through the pilot and main jet air passages aswell. With the mods done to your engine changes may be needed in the air jets located at the bottom intake side of the air horns. There are 2, one for main, one for pilot. If they are not functioning properly jetting changes could be futile. For giggles toss on a set of air boxes and give it a whirl. If things change for the good you know you're on the right track. Pods might do the trick?

Could be the reeds and I think I've read somewhere that those carbon fiber reeds weren't all that great. Not sure but toydo's suggestion of swapping them out would tell that tale.

One other thing is pipes. I know you've run two different sets and still have the issue but one thing I've noticed with just about every Vmax-4 I've been around is that they like hot pipes. Trying to race or dyno one with cold pipes always seems to create a stumble when accelerating so if you're not warming the sled good before a run cold pipes could be the issue.

Again, don't have any real answers for you just tossing darts at the wall with what I know/think and what you describe.

Good Luck, opsled
 
Thanks again guys. I have gone through the carbs many times. I've stripped them down as far as I can to clean and synchronize. I have changed the mains and pilots, but I will take a closer tool at the o rings under the needle/seats. I have another Stock carb rack that I may try. I always run with factory gutted airboxes installed.

The plugs are all basically the same, and looking good.

The only belts I run are Yam 8BU. As I mentioned in an earlier post, I have measured the air gap between the belt and sheave, at a approx. 0.040". I changed out the split collars to achieve an air gap of 0.020". I will test tomorrow, with crossed fingers!

As for the hot pipes, the bog seems the same regardless of pipe temperature.

Again, I really appreciate all the suggestions here. I have NEVER had a sled give me this much trouble to set up. I'm hoping it's all worth it in the end......!
 
Had a 600 do this after porting and GYT pipes. It was the reeds on that one.

When I drop from .040 to ,020 gap, Im looking to take the shock / wack out of clutch engagement. Not really a bog. If anything .040 gets a running start at the belt and grabs.

Check to make sure your not sucking the belt down into the driven clutch on the launch. Twist / tighten it up and retest, see if it helps.

You have the right CDI for you pipes (and chip if it has one)
 
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Thanks toydoc, I have changed out both primary and secondary clutches and tried different springs/helixes options. I am headed out this morning to test again with the split collars changed. I have also removed the boost bottles and plugged the holes, as this was suggested from a very experienced engine builder as well.

I am running a stock 96 800 CDI. I have tried Stock timing, as well as adding a timing key. I will keep you posted
 
you covered this sled like a glove. woody, right before your holeshot, flick the choke on and off fast. just to see. 3:16x (yammie tony)
 
Tried that too, no luck. Even up on the stand it was bogging without any load.

After speaking with Justin today, I fired it up with the airboxes and primary clutch removed. It ran perfectly, zero bog. Leads to back to clutching.
 
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