ATC 90 performance upgrade possiblities

[greenhuman]

[QUOTE=turbowrenchhead;843758]I looked at that carb. Where is the choke on it? The seller has only one pic of the carb.
If I don't win that carb what would be an alternative? Is the 22mm carb on DrATV.com a good deal?

A standard '83-'85 ATC125M carb and an ATC110 manifold would be the other option.
The lever on the side of that Ebay carb is the choke lever.

[turbowrenchhead]

Greenhuman. Their is already a 22mm carb on it. Question is what is it off of? Check out post

http://www.3wheelerworld.com/showthr...-on-the-atc-90

Ok. I have another question. I filed the points and gapped properly. They were out of adjustment. I adjusted the valves. The intake was too tight and the exhaust was too loose. I went to time it and I don't see any marks on the points plate or anywhere. The manual says either a T or and F to line up with the case mark.
So how do I time it when I don't have timing marks.

Check this post to see pic.

http://www.3wheelerworld.com/showthr...485#post844485

I was also wondering why the rear brake is linked to the chain tensioner on these? I don't understand why you would tighten the chain when you applying the brake. Does that act like a brake?

[greenhuman]

The T + F marks are on the flywheel. Take off the zippy then the three small bolts holding the zip start plate on the flywheel. You will see the TF marks on the flywheel. If you look on the stator you will see a small scribed line (about 3mm long on a little extention)
The T mark is for cam timing and the F mark is for spark timing. The idea is to turn the engine over by the 14mm bolt in the center of the flywheel by using a wrench. The points are supposed to be just starting to open when the F mark is in line with the mark on the stator. Loosen off the two phillips screws holding the points backing plate and turn the plate till the points start to open when the marks are lined up then tighten the screws. Check your points gap and that should be it.
Looking at your points image, the timing looks retarded.
The carb looks like an ATC110. It should work OK.

[jb2wheels]

I was also wondering why the rear brake is linked to the chain tensioner on these? I don't understand why you would tighten the chain when you applying the brake. Does that act like a brake?

The rear brake and chain tensioner are not actually linked. The brake pedal pivots on the chain tensioner shaft. The chain tensioner actually has a lock down bolt on the RH side of the frame behind the brake pedal.

If pushing the brake pedal tightens the chain, the pedal is siezed on the shaft or the chain tensioner is not locked down.

[turbowrenchhead]

Thanks for the info guys. I will see what I can do.
Moving the points plate clockwise will advance it or retard it?

[Walkerallen]

moving clockwise will advance and counterclock wise will retard

[turbowrenchhead]

Found the marks, timing was retarded. Corrected the timing. Would you want a little bit of advance timing or should it be set per manual?

[greenhuman]

Alittle bit of advance. Make sure your advancer behind the points plate is working properly as well. You can turn the lumpy part a little bit and it should spring back.

[turbowrenchhead]

I will check it today, thanks.

[Jeepermc]

Subscribing for interest....Good thread

[turbowrenchhead]

This is what I asked DrATV

I am interested in replacing the piston in my ATC 90. Correct me if I am wrong.
The stock compression ratio is 7.5:1 with a 50mm bore.
Your big bore piston is 9:1 with a 54mm bore.
By looking at pics of a stock piston and your big bore piston it looks like their is more of a dome on the 54mm.

Powroll sells a 54mm piston that has a 10.5:1 compression ratio. That is a little to high to run 93 octane fuel, one would need 95 to 100 octane to offset pre ignition problems.

Is this information correct?

This is the answer I recieved

well because of the more volume the extra 4mm develops, my unofficial guess is our 54mm piston will be in the hood of 8.5 to 9.0 comp.

yes all you need is to have you cylinder bored out and a stock gasket set.

yes because of the head's dome design the stock head gasket will work fine

i like to have .0015" piston to cylinder clearance

What is up with this guy? How can he advertise 9:1 when he doesn't even correctly calculate the compression ratio?
For example:
1. Determine the displacement of your engine. Displacement formula is:

BORE X BORE X STROKE X .0031416 = DISPLACEMENT

Example: 92 x 92 x 82 x .0031416 = 2180cc

2. Determine the swept volume of one cylinder:

Example: 2180cc divided by 4 = 545cc

3. Determine the deck volume of each cylinder. The deck volume is the distance from the top center of the piston to the top of the cylinder when the piston is at top dead center. Measurement is made in thousandths.

Example: on cylinder #1 you measure and find you have .020" deck height.

BORE X BORE X DECK HEIGHT X .01996 = CC"s

Example: 92 x 92 x .020" x .01996 = 3.378cc's

Measure each cylinder.

4. Measure the volume in each cylinder head. To do this, use a piece of plexiglass cut to fit in the cylinder head to cylinder mating area. Drill a 1/4" hole in the center of the plexiglass. Lightly grease the edge of the plexiglass and install in the head. (Spark plug and valves have to be installed) with a syringe graduated in cc's fill the cylinder head chamber up with a light weight oil. Record the measurements. Repeat for other three chambers. Average cc volume of a new head chamber is between 47 and 51 cc's.

5. You now have all the measurements to determine your compression ratio.

one cylinder swept volume + deck cc + head cc

deck cc + head cc

Example: 545 + 3.378 + 48 = 596.378

3.378 + 48 = 51.378 = 11.6:1

[Vealmonkey]

turbo, in a way you answered your own question. But pump gas shouldn't be a problem at 10.5:1. And the powroll does have a sllighty higher dome than the old tucker rocky pistons. I remember you asked about shaving the head. The 2 big problems with that are 1, once you shave your head and add a domed piston, valve and dome clearances become super critical and 2, sometime shaving the head or cylinder can have bad results with the overhead cam chain. Now you sound a tad bit more knowledgeable than the some of the people on here. So I'm thinking that you have dealt with piston and valve clearance types of issues before, maybe many times before, so that gives you a major leg up on some of the people on here. But there are people on here who would shave or deck their piston and cylinder or have them shaved or decked and then install the piston and put it all together without checking and then have disasterous results. Obviously you have engine building experience under your belt. But, before shaving or decking or however you would like to refer to the operation as, please check your clearances beforehand and see how much you have to work with. With manufacturers tolerances and 30 year old engines and aftermarket gaskets, your margin for error may be quite slim. The average person on here who is putting a new piston in a 90 on here is not really gong for performance gains and is just trying to get a fresh bore and piston. There are a couple people on here who dabble with old 90 power. There many neat tricks to do to a 90 engine. Motorcycle pistons and all kinds of other magical things. But the main reason I believe that you are not getting alot of responces is that not too many people do these kinds of things. You know how to cc a head. I would take it that you know how to "blueprint" an engine then. Your best bet is to blueprint your 90 engine out. Matchport your intake to your head. Polish your inlet port and exhaust port. Beware of opening up your exhaust port, as this will more often than not kill what little power your engine has. You can balance your rod and piston if you so desire, it will add a little extra power. I know people who have redcoated the insides of their engine cases. I know of people who thermal coated their pistons. Some people wrap their exhausts. Some people vent their heads, highly recommended on engines that will constantly turn high rpms. Remote oil coolers and way more crazy and anal mods. But you also listed that you are mainly using the trike to pull an ice shed if I remember correctly. You really need a cam that makes your power on the low end for that or so I would think. But really I would think that a larger engined trike would work much better for that, in my opinion anyway. I"m not trying to discourage you in the least. If you remember I was the one that suggested that you get your trike in top notch running condition first and then go from there. The 110 carb and intake was one of the most simple and at the time economic hop ups to perform. Now that parts are 30 years older and harder to find, it's a tad harder for that to be an easy mod. You can still find aftermarket intakes and larger carbs, but it's a tad bit tougher to find them and a larger carb only works well with a cam, a larger piston and a better filter and exhaust. And the majority don't really want to spend the time and money when it's easier to just get a larger displacement trike. If you are wanting to go crazy, having your cranked stroke and running a sleeve and a cb750 piston is starting to get you in the ball park for serious 90 power. Changing engine cases is highly recommended so you can get rid of the hi/lo gearbox and go with a manual clutch. But I'm not sure how crazy you really want to get here. But there are tons of mods for the dedicated.
Oh, and before I forget, the poor guy is just selling pistons, not performance advice. LOL

[turbowrenchhead]

My goal was is to add just a bit more power. I'm going to put the 54mm piston and a cam in it. But Dratv is out of cams for now. When he gets some in I will order the piston and the cam and valve springs. The piston rings must be bad because the thing smokes like crazy. I will port match and polish everything at that time. I lost the auction on ebay for the stock exhaust. I'm trying to find something that is priced right for it. I just ordered a new 22mm carb for it. Their was already a 22mm on it but I've had it apart 4 times and its still acting up. Plus the pilot screw doesnt work on it. The stock intake was at 16mm so I opened it up and polished it inside. Over the last two days I have went through the manual and I have made all of the adjustments that I can do. Today I have to get the front tire apart again, it leaks. I have a inner tube for it.
I think if I do the piston and the cam the trike will have enough power for what we want it for.

[turbowrenchhead]

After I tuned it up we took it out yesterday. It had more power then the previous sunday. But I had to retard the timing from where it is suppose to be. What could cause the marks to be off?

[shortline10]

After I tuned it up we took it out yesterday. It had more power then the previous sunday. But I had to retard the timing from where it is suppose to be. What could cause the marks to be off?

32 years old and a worn timing chain / cam EXC