1976 Nitro Grass Drag Set Ups

[mrmotors]

If I've done the math correctly, based on 6", every .052" of movement at that diameter is equivalent to 1 degree of crankshaft rotation. Maybe that will help with timing... That is based on 6", if it is something other than that size, it will be different.

[mrrupp1]

Hey midniterupper just wondering how the nitro drag sled is coming? Have you down any testing yet? Hope everybody had a good Thanksgiving. Clint

[midniterupper]

Hi Clint, Thanks for your message, sure appreciate your continued interest with the sled. I have been busy around here getting my pre-winter tasks done for the farm. I ended up picking up a 1937 John Deere model B tractor a couple of weeks ago at an estate sale, it didn't run at the time but I got it going. It's a hand flywheel crank, took up too much of my time so it is for sale now.
Now, I was able to sneak in some work to the sled in between chores. I was also able to work on the test lane that we made this past summer. We made it wider and smoother, should be a bit easier on the sled. Much better for testing!
Regarding the sled work, I did a squish reading (.070" on both cylinders) and I did a compression test, 150# on the PTO and 151# on the MAG side. Pretty happy with that for now. I installed another CDI unit that I purchased from a guy on line. It is used but in good shape visibly, I cleaned the connectors and plugged it in. The sled fires up and runs the same as with my original CDI, still can't seem to get above 7400 rpm but I guess I really didn't think it would matter too much in that regard. Good to have a spare in the parts box!
I also got out the dial indicator to establish TDC on the mag cylinder. Scribed and painted aligning marks on the clutch and the side of the engine case. I marked it at TDC and also at .100" BTDC. I started the engine with the sled on a stand, revved up beyond 6,000 and actually witnessed the timing marks advancing. Pretty cool! I still need to verify the static timing on the flywheel/stator to make sure it's where it needs to be.
I removed my carbs to see what we can do there and document what's in it. The floats were set pretty close to spec, the pilots are #45, the slides are #2.5, and the needles are 6DH4. I had 310 mains in it but the spark plugs look very dark and oily so I will install 300's. I called Kevin at Pipestone to ask what he has for his carb set up and he is running 1.5 slides, #50 pilots and much larger mains, but his sled has stingers with no cans. I would like to pick up a couple of 1.5 slides to see if the rpm's pick up quicker. I'll get some #50 pilots to try sometime as well.
Tomorrow I want to remove the belt and see how the rpm's respond being unloaded, maybe it'll be different. I will let you know. I need to verify my clutch alignment is correct also.
I've been meaning to ask you what kind of oil do you use and what ratio? I've been using Ski-Doo mineral oil at a ratio of 40:1. I haven't had any issues, just seems very oily around the exhaust couplings and spark plug holes. Which brings to mind another question, what kind of spark plugs do you run with? I have been using BR9ES solids with my gap at .020" Would you recommend something else? Do you think indexing is worth the extra effort with these motors? Wasn't sure on that one either.
Okay, I've taken up enough of your time tonight. Please let me know what your thoughts are and I'll be sure to let you know our progress. The snow is now deep enough to begin testing again, it'll be a little different but I guess the sled will run in the snow eh?

[mrrupp1]

I use BG two stroke oil, it is a semi syn blend. I mix it 40:1. BG is a Oil and fuel additive company primarily for the automotive world. There product is top of the line stuff. As far as spark plugs I use the NGK BUE surface gap for my trail sleds and for my liquid race sleds I use NGK B10EV. On a different note I collect John Deere two cylinders. I love to have that 37 model B tractor. I have 49 John Deere R, 39 John Deere A and 52 John Deere wide front end 50. My brother has a 31 John Deere D and a 47 John Deere G. As far as indexing your plugs I have never done it so I don't know if it would help or not. Please keep me posted. Take care. Clint

[midniterupper]

Hey, thanks for your reply and all the helpful tips that you share. I am not familiar with the BG brand oils but I will look around for it. Your 40:1 ratio will provide good lubrication, I think that insurance is worth putting up with a little oil around the exhaust so I will stick with that ratio also. I've never tried the BUE style spark plugs before, once I get things settled in with the sled I will install a set to see how they work out. I still have my carbs off the sled to do a little lathe work to the intake flange and I still need to pick up some mains and pilot jets yet. I also ordered a Polaris Almond/Gold primary spring, it was back ordered but should arrive today. It'll be ready for testing.
I've got a great offer for you if you would like the old '37 Deere, I would love to see you get it for sure! We'd have to make arrangements for you to get it but it's certainly possible. $1200.00 for you, it includes a 24" buss saw (attached to the front end, driven by the side pulley) also a 6' snow pusher blade, tire chains, a rear push bar, extra leather drive belts, lubricants, a box of old ignition parts and a shop/owners manual that we bought for it. That's the price we paid for it, he wanted $1800.00, it was always stored in a barn so it is in really good shape. Original paint too! Would love to meet you and kick around some ideas. Let me know if we can work something out. Thanks again for your interest Clint, that's pretty cool that you're into that stuff as well. There is a big antique tractor and steam engine show right up the road in Buckley Mi. Type it in and check it out sometime, 3rd week in August, 4 day event.
Better get busy here, I'll keep you posted on the progress. -Paul

[mrrupp1]

I think in your race sled I would run the NGK B10EV there easier to read the plugs and that's what Rupp recommended in there race sleds. A lot of people do not like the surface gap plugs at all. They are hard to read to see if your running rich or lean. They do work good for my trail sleds. I'm going to have to pass on the B. I'm going through a estate settlement with my two brothers and it's getting pretty ugly. Thank you very much for the offer that would be a sweet deal. Take care talk to you soon. Clint

[midniterupper]

Hey, thanks for the advice on running the 10's for plugs. I'll pick up a few to have them ready for testing. I had a mishap while turning the intake flange on one of my carbs, ended up cracking the intake side of the carb. Bummer! Never had that happen in 45 years of machining but I should've known better, oh well. I called Kevin, he's got a set carbs that would be a nice fit. I think mine are 38mm, gotta get out my digital calipers to make sure they are.
I understand about your situation regarding the B. I'll have it for a while I'm sure due to the weather now, but it would help justify a road trip to come see ya! Take care now Clint, thanks again for your help. -Paul

[Ruppsforever]

Like Clint said I always ran B10EV plugs too. I always ran Amsoil 50:1. But as far as I'm concerned you aren't going to see any gains or losses on different kinds of oil. If I still raced I would use a different oil and run it at 40:1. A little more oil makes a little more power if jetted right. The oil seepage on you're exhaust flange will always be there. These motors like a lot of gas on the low speed circuit on the carburetor. If you try to lean out the pilots or needles or cutaways there will be a bog. Perhaps you have a bog already because of your different carburetion ?? If your main jets are dead on you won't have any seepage at wide open throttle but it will always come back once it sits there and idles.

[Ruppsforever]

When you had the timing light on it where did it look like it was ?? Like halfway between TDC and .100 or was it closer to .100 ?? Stock timing on a 440 is .085.

[midniterupper]

Hi Josh, thanks for your reply. When I set up the timing light, I made marks on my clutch O.D. when at TDC which aligned with another mark I made on the crankcase bearing area. Then I backed off the piston (using a dial indicator in the mag spark plug hole) until it read .100" BTCD and then I made another mark on the crankcase using the same scribed line on the clutch. When I fired up the motor, at idle the mark kinda hung out closer to the original 0 degree mark, but not right at it. As I increased the RPM to about 6 grand, the mark advanced closer to the .100" mark but more like 3/4 of the way to that mark. Which is making more sense to me now that you clarified the stock timing spec. I will scribe another mark at .085" to verify it (good experience!) but I would like to try your advanced setting, I think it would help produce more ponies.
I definitely will run with the NGK 10's. Do you think we should run with resistor type? I have some BR9ES and some B9ES plugs here in the shop. When I put the new plugs in a spark plug tester, the non-resister plugs appear to have a much brighter spark than the resister type. But I never ran the non resister in the sled itself, wasn't sure how they could affect the CDI unit so I didn't try them out. Regarding oil, I'll try the semi syn blend out, seems more slippery when playing with it. 40:1 sounds like a good ratio also. As they say, Oil is cheaper than pistons!

[nitrofa340]

For what it is worth,...everything I have researched and read says that a 32:1 ratio generally makes the most power in most 2 cycle engines. It is pretty much accepted as fact by most sources that MORE oil in the mix ratio actually results in more power due to better/more efficient sealing of the piston rings. I just always liked the idea of more oil in the mixture. Feels safer that way.

[midniterupper]

Far out! Never really thought about all the advantages of oil in a two stroke beside just the basic lubrication qualities, but helping seal up the piston rings certainly makes sense too. I've never ran quite that rich, except back in the early 70's with 20:1 in our old Hodaka's which still ran points. Will that mixture foul plugs more easily or will the increased output of the CDI burn through it? I went through a lot of plugs and kick starters back then with the old ignitions.
Now when I go to advance my timing, I wasn't sure if the stator plate had slots or if it was a fixed location? I had a old Honda 750 that I did some performance work to a long time ago and in order to advance the timing over stock, I had to physically cut slots in the stator plate to allow the advance. Not sure if the Xenoah's follow the same procedure.
The carbs I'm considering from Pipestone are bored and ready to go. He didn't say how much they were bored, I guess they were the original 38mm and maybe bored to 39.5? I wasn't sure if they would be a good application for my sled though. I have never tried dialing in something like that though I imagine we would just follow the standard procedure of starting rich and working my way down on jetting. Do you guys think there would be a significant gain for drag racing? Pretty big difference in cost of those carbs (which is more than fair) verses just buying 1 used 38 at a salvage yard. Christmas is coming so it is a possibility, I think I have been good this year!

[Ruppsforever]

I agree 100% with what Dale says. 32:1 has better HP with proper jetting. I tried mixing amsoil richer but there was oil puddles all of the place. Amsoil's recommended mixing is only what it can be mixed at. 39.5 carbs are what I always used on my 440 and 340 mod motors. Not sure if any gains will be made on a stock motor.

[midniterupper]

Hey, Just a real quick update here for my Nitro. The Polaris almond/gold spring arrived yesterday, also picked up another 38 mm carb. It didn't have any slides or jets, so I just swapped out mine, installed #50 pilots, removed the #45's. Set the air screw at 1.5 turns out. Verified the float levels, installed the carbs, sounds about the same as it did. Maybe a more crisp idle. Topping out on the stand at 7400 rpm, which is okay for now. That will be my next focus.
Installed the new primary spring, engages at 5400 rpm. I like it! We will do some testing with that one, should be a good improvement over the Comet Green/Yellow @ 4800 rpm.
Another question now that it's cold outside. Should I be running a thermostat for drag racing during either summer or the winter? I wasn't sure, I always make sure the motor is hot before revving it up, but there wasn't a thermostat in it when I got it. Thanks for the info! -Paul

[airron0075]

I think you shoud tighen your secondary clutch up untill you get the rpm you want It would be Ideal if the rpms go up to the rpm want right away and stay there all the way through the shift and if you have it right you can let off the gas and
pin it and it goes right back up to the rpm you have it set for
I have a 1977 rupp nitro that I put a artic cat secondary on it I think it is to tight it reves to high and is not going that fast I think my chan is jumping to I am going to try your trick for that

[mrrupp1]

I think thermostats are a good idea because it keeps the engine temp regulated which we all know is what we want . But Two of my nitro liquid trail sleds don't have stats and they run around 140, which is where you want them. I have a 340 liquid nitro with a thermostat and it runs a around 140. The oval track sled I run a stat, but in a drag sled I don't think I would. That way you can cool it down between rounds. Thats the way I run my drag car. We have an electric water pump and run the water pump with a fan on the radiator while the engine is off. My liquids run the best between 120 to 140 anything over that they tend to heat soak. This is just my opinion, I'm sure there's guys that know way more then I do. Clint

[midniterupper]

Thanks Clint, that makes sense with the fast cool downs we need between rounds. I haven't had a problem without running one so far, at least in the summer/fall season, the temp seems to stay pretty steady for me with our short runs. I use a temp gun (along with the hot hand method!) and it reads between 135-140 degrees after a run, and we're usually around 120ish just before we launch. Still using the bumper for heat distribution as well, I learned quickly to just grab the ski tips when moving the sled around at the finish line! Now for the winter season, I think I will go ahead and run with one as you mentioned. That should help keep temps more consistent, easy enough to keep track of. My engine temp gage doesn't appear to work, but neither do the lights lol.
Glad to see another Vintage interest with input from airron 0075. Hopefully he will also appreciate the expertise you all have offered for everyone on these forums. The support and encouragement is second to none, along with the wealth of experience and wisdom you all have shared is what continually amazes me. I'm so glad this message board exists, I'd be lost without it!
Did not get a chance to work on the clutching today, went to the salvage yard to pick up some parts for future testing. Think I will replace the plastic chain tensioner pucks with rollers. Will still employ the fixed tie-bar concept for sure, it works great. Until next time, -Paul

[Ruppsforever]

A thermostat will help the motor warm up faster to operating temp. That is the only gain to be made with a thermostat. Once the motor is warm having one or not having one doesn't make any difference.

[midniterupper]

Excellent! No harm done then without one, I'll just make sure the motor is nice and warm before any full throttle runs. Don't want any cold seizures. Besides, running without one should make that front end lighter! Can't wait to get back at it....

[midniterupper]

Okay, finally had some time to work on the clutching situation today. Warmed up the sled on the stand. With the track off the ground, I can rev up the motor (with the drive belt on) like I have always done and the RPM's still topped out at 7400 RPM, which is pretty much normal for it.
I then removed the belt from the clutches and revved it up again. 8500 rpm with no problem! Not sure what this means though. The tack definitely is working, when I rotate the track by hand using the secondary, it doesn't feel like too much drag.
I haven't changed my clutch arms (Comet A-2 @ 48.5 gr.) since we had our top speed run of 67 mph. The RPM on playback was still at 7400 on that run also. I now want to focus only on my clutching getting the R's up to where we should be. Of course I have many little projects in store for the sled, but I think we are at the point where the sled can win (at least on grass!) at 67 mph, as that was the fastest time we recorded with radar for the vintage classes. I'm thinking once we get our rpm's up to 8300, the sled should be even faster. Then I can begin playing with secondary helixes.
For Christmas, I think I'll be getting a Koso digital tach, with (2) EGTs and water temp sensors. Has anyone installed one of these units on their sleds? Let me know what you think of them verses the Digitron units. Thanks again! -Paul