bunch of Grubee GT5 questions

GearNut · Aug 3, 2010

The mag rotor is held in time by a woodruff key. If the key is missing or somehow gets sheared, even partially, it will definitely affect the ignition timing.
A very common error in rebuilding these engines is installing the rotor backwards, or inside out on the shaft. The rotor will go on either way and if one does not mark the outside face of the rotor with a marker or whatever, it is all too easy to re-install it backwards. A backwards rotor will also put the timing off.
If the rotor was not marked before disassembly, you can verify that it is correct this way:
With the magnets setting horizontal (left to right) the keyway will be in the 1 o'clock position.

If the keyway is in the 11'oclock position the rotor is backwards.

Why on earth the Chinese couldn't machine the keyway to be in the 12o'clock position is beyond me. If they did then it would not matter which way the rotor fits on.

jauguston · Aug 5, 2010

Andy,

Needle clip in the middle is a bad sign. Put the clip in the top groove. Even there it will be a little bit rich. If the clip is actually in the middle you are drowning the engine in fuel. Does your carb have the square red aircleaner". If so you are going to find the main jet is too big also. Stock is a 70. I tried a 68 and it was better and I am now trying a 66. SBP has jets.

Jim

GearNut · Aug 5, 2010

Clip in the middle position is the factory setting and works out quite well for some engines. They are adjustable to accommodate differences in engine tuning and altitudes. Also the quality control sucks with regards to jet size and needle taper so adjusting the clip is common. To immediately set the clip to the leanest position (top groove) could spell disaster. A too lean of a mixture can overheat the engine and potentially burn a hole in the crown of the piston.

jauguston · Aug 5, 2010

My Grubee Sky Hawk 66 from bikeberry came with the carb that says "SPEED" on the side and it came with the clip one groove from the top. It would four stroke at all partial throttle settings and took a little while after I opened the throttle fully to finally smooth out and run clean. As soon as I reduced the throttle below full throttle it would go back into four stroke blubbering. I moved the clip to the top groove and that made it better but it is obviously still too rich. When I get time I will set the slide up and cut the place the clip rests down another .030 or so. I now have a 66 jet in the carb and it is getting better.

I would guess the guys that run a fat oil content might not be as rich as those of us that run 100-1 because their fuel will be thicker and not flow as easy.

Jim

andy b. · Aug 5, 2010

Thanks for the continuing ideas!!!! I wasn't able to play around with the bike the past few days, so no updates. Tomorrow I'll have a chance to work on it again and I'll try to level the carb and play around with the needle setting.

andy b.

GearNut · Aug 5, 2010

jauguston said:
My Grubee Sky Hawk 66 from bikeberry came with the carb that says "SPEED" on the side and it came with the clip one groove from the top. It would four stroke at all partial throttle settings and took a little while after I opened the throttle fully to finally smooth out and run clean. As soon as I reduced the throttle below full throttle it would go back into four stroke blubbering. I moved the clip to the top groove and that made it better but it is obviously still too rich. When I get time I will set the slide up and cut the place the clip rests down another .030 or so. I now have a 66 jet in the carb and it is getting better.

I would guess the guys that run a fat oil content might not be as rich as those of us that run 100-1 because their fuel will be thicker and not flow as easy.

Jim

The needle controls the air/ fuel mixture between just off idle to 3/4 throttle.
Changing the main jet size to effect the fuel ratio that is controlled by the needle will have you chasing your own tail.
If you are still having blubbering problems above 3/4 throttle than definitely go to a smaller main jet.
Your idea of creating another groove to lower the needle even more may work out well for you, just be careful that the fuel ratio does not get too lean at idle to less than 1/4 throttle.
If you can, get a different needle with a fatter taper to it. You seem to be fighting a mismatched needle that is just too skinny to work well with the carburetor, or a needle jet that is too big for the needle. The needle jet is the long brass tube that the main jet threads into the bottom of and the needle slides inside of. It is possible to fill in the needle jet with solder and drill it out to a smaller size. You only need to do this in the top 1/4 inch or so, not the whole length of it.
I would chalk it up to poor quality control at the Speed carburetor factory.

andy b. · Aug 6, 2010

I had some more time to play around with the engine today. As near as I can tell the magnet for the magneto is where it should be, and I do have a good spark. I lowered the needle and put the clip on the top groove. I don't know if I have the same carb problem as Jim, but even on that top setting, it appears the engine is still running way too rich. A neighbor and I were playing around with it and when I would try to get it started we both agreed it sounds very rich. With no choke, and no priming, when I go flying down the road and let the clutch out the engine will sputter and buck and tries to run a little. It actually was running a little bit, but as soon as I slow down and pull the clutch in it dies. The head was slightly warm to the touch, so the engine was at least running in spurts.

Could one of you provide a description of "4-stroking", because I think that is what it is doing all the time.

I didn't have time to pull the engine out and make a different mount to level the carb, but I think that may be the cause of my problem. Tomorrow I am going to try to make a new mount and also take the carb apart to see if anything looks wrong inside of it.

I have another question. It may be easier for me to modify the intake versus altering my mount. Would there be any problem with modifying the intake, or would it be best not to touch it?

andy b.

GearNut · Aug 7, 2010

It is perfectly acceptable to mod the intake manifold anyway that will work. Just be sure that you do not have any air leaks.

4 stroking:
YouTube - ‪What is "four stroking" ?‬&lrm;

andy b. · Aug 7, 2010

GearNut,

THANK YOU!!!! After watching that video, I think my engine may be six-stroking or even 8-stroking.

It looks like today's project will involve the carb and/or mounting issues. I'll report back what I find.

andy b.

Flight Risk · Aug 9, 2010

GearNut said:
The needle controls the air/ fuel mixture between just off idle to 3/4 throttle.
Changing the main jet size to effect the fuel ratio that is controlled by the needle will have you chasing your own tail.
If you are still having blubbering problems above 3/4 throttle than definitely go to a smaller main jet.
.

My bike runs perfect at idle and up, untill I get to full throttle above 25mph. It almost seems like a speed governor kicks on, or the valves are floating (if it were a 4 stroke). It just won't peak out smoothly. I'm guessing it leans out, and I was going to try and adjust the needle, but if that only has affect up to 3/4 throttle it may not be the cure. I'm at 6,000 ft. and am try to think that if we have less air, then we need less fuel, but that may be reversed thinking. Also the instructions for my Grubee mention an air mixture screw which is preset at 3.5 turns out, but I believe this is actually the idle screw. It then says if a more rich mixture is needed the "pac man" clip can be moved to the next lower position. But will that affect the top end?
Also I wonder if anyone has tried putting a Walbro type carb on these bikes. They seem more tunable with high and low speed mixture screws.
:-||

Rod S

jauguston · Aug 9, 2010

Rod,

Not what you want to hear but it is "possible" that at 6000' with the lower air density you may be getting all the HT has to give. I am at sea level and 29-30 mph on flat ground is all my Grubee Skyhawk 66 will do.

Jim

Flight Risk · Aug 9, 2010

It seems there is more as sometimes it revs out then starts hiccupping. also downhill it just won't wind out.

Rod S

GearNut · Aug 9, 2010

At 6k feet elevation you thinking is correct. The air is less dense so you do need to reduce the amount of fuel being delivered to the incoming air at a proportionally correct ratio of 14.7 to 1
good luck getting it there. The best thing to do is a "plug chop". It needs to be done in the engine RPM range where the problem arises. Operate the engine at this aggravating speed for a mile or so then simultaneously kill the ignition and pull in the clutch. Whatever you do, do not let the engine even pop or burble under it's own power as doing so can ruin the "chop".
Coast to a stop (the test is best done on your way home) and let the engine cool down for at least a half hour or more. Remove the spark plug and look at the electrodes. The color of the center porcelain should be a chocolate brown to a leather brown color. Black is too rich, pale tan or white is too lean.

I highly suspect that you are too rich right now and a re-jet is in order.
If you cannot find jets you can always do the solder and drill trick.
Set the jet on a soup can lid and place that on the stove. Heat the jet until you can melt solder inside it to fill in the metering hole in the jet. Use fine wire drills and a pin vice to now create your own smaller sized metering hole. Yes, this method is trial and error, but it works remarkably well.

Edit: that screw you are talking about is an idle speed screw.
Walbro carbs have been successfully adapted to work on HT engines.

andy b. · Aug 9, 2010

Latest update:

First, don't even bother messing with the intake if your engine is not level. The intake is such that the carb is as low as it will go without hitting anything. If the carb sits low and you need to raise it, you can probably do that, but most of the pictures I looked at showed the carb slightly high. In my case it was high.

So after playing around for an hour and finding no way to modify the intake, I just welded up a new rear mount. I should have did that first, but I liked how the engine was sitting in the frame. Now I know better.

I got the engine pretty level and I think it still sits good in the frame.

I took the carb apart and everything was nice and tight in it and the float, needle and jet looked good.

I also verified the magneto magnet. I took the magnet off and the key is kind of sloppy. I'm not sure how much this would affect things, and I may end up making a new key, but I don't think that is my main problem.

So, I got everything back together and it still does the exact same thing. The c-clip on the main needle is at the highest setting. If I put the choke on, the engine won't even attempt to start and the spark plug comes out wet. If I leave the choke off and head down a hill in front of my house the engine will start blubbering and really bucking if I keep it around half throttle. Once I start slowing down the engine dies, and it won't go any faster when going down the hill. Honestly, it sounds way worse than the 4-stroking video posted earlier.

Can any parts of this kit be used with a Morini engine? I am getting to the point where this engine is going to meet a sledgehammer :-||

and I'll stick one of the Morinis in instead. I may try the soldered jet and re-drill trick. Any ideas of what size drill bit I need to use to open the jet back up?

Is anyone in the Allentown/Lehigh Valley area available Saturday for some experimenting on a Grubee engine? I can provide beer.

andy b.

KCvale · Aug 9, 2010

I just don't know Andy...
The original problem may have been the motor angle, maybe not, but you may have even 'fixed it' to death.

Try this:
Pull the carb and tailpipe and turn the cylinder to the bottom so both ports are open and let it sit protected from the weather so any gas in the crank will evaporate for a day or two.

Then, put the carb back on without the air cleaner and leave the tailpipe off.
No choke, but pedal and keep working the throttle full to off and see what happens.
Remember, these direct drives won't run engaged under about 10-12MPH because of the gearing.

If you get it going, keep it going! Keep pedaling to help if need be.
It will be loud as **** but that eliminates a simple clogged tailpipe as your culprit.

If you can keep it going without using the clutch over 15mph until it warms up, then you can mess with other stuff.
If not, well, I am flat out of ideas bud.

andy b. · Aug 9, 2010

KC,

I can try that. I thought on the 2-strokes that you need the exhaust to provide a back-pressure pulse to help compress the air/fuel mixture in the engine? At least that was the reason I heard for the crazy shape of 2-stroke tuned exhaust pipes. I didn't even think a 2-stroke would run without an exhaust pipe.

I picked up a speedo/odometer for the bike (anticipating that it would actually be running) and I think I'll install it to see how fast I am going when I try to engage the engine. There are two bigger hills near my house so I can "take it up a notch" as the case may be. I'll get it up to 15MPH or so and see how long I can keep it there. If I was a little crazier I'd let my wife tow me around with the car, but I somehow sense that would be a good method to end up with serious injuries.

One way or another this bike will have a running engine in it by the end of the summer.

andy b.

er0401 · Aug 14, 2010

I "had" the same problems as you, i still do but my chain broke possibly by stress, I have a big hill that i am gonna go on when i get a new chain and pray to god that the **** thing works!

andy b. · Aug 15, 2010

I had another go at it today, with the exact same results as previous attempts. I didn't take the exhaust off, as I'm not exactly sure what would happen, but I installed the speedometer. I was getting up to 15MPH and releasing the clutch. And again, if I would choke it, the engine would not even attempt to run. If I left the choke off and got up to 15MPH, the engine would sputter and buck if I kept it under half throttle, and keep doing that as long as I was over about 12MPH. As soon as I would pull the clutch in it would die.

A friend suggested spraying a bunch of ether/starting fluid in it and seeing what happens. Should I give that a try?

I am nearing the end of my patience with this thing.

andy b.

jauguston · Aug 15, 2010

Andy,

Don't give up. There are thousands of these little motors out there running like a clock. There is likely some little thing you are missing. Have you tried finding someone with experience with small two stroke engines to help you. There are so few systems there it can't be anything complicated.

Your description sounds like it is rich. Have you tried shutting the fuel valve off when you get it running to see if it will start running better as the fuel is depleted?

Jim

Flight Risk · Aug 15, 2010

I'm curious if setting the float level has any affect on how rich/lean it runs? I had mine apart an noticed it wouldn't take much to bend the tangs on the fuel shutoff lever thing. I've rebuilt many carbs and it seems you are always requred to measure the distance of the float. Do any specs come with the carb rebuild kit?

Rod S

bunch of Grubee GT5 questions

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