CR 125 Mod Results

[Jay-R]

Okay, for those who are interested, I finished my CR today and got to ride it. Here are my mods:

Vertex piston for Husqvarna 125 (53.94mm)
Cometic high compression gasket set (thinner base gasket)
Power valve spacer
V Force reed cage
Shortened factory silencer (cut down 50mm)

I am running 50/50 mix of 110 octane race gas and 93 octane pump gas. I turned my air screw to 3 turns out with the needle on the second groove.

"SEAT OF THE PANTS" RESULTS

After the heat/cool cycles of break in, I had a chance to ride around my field today. I am happy, not by an amazing power increase, but by the increased width of the powerband. Before, the CR was a midrange only motor. When exiting a turn, you had to clutch, rev and the rear wheel broke loose then try to shift before you ran out of midrange power. Now the power is much easier to control. It comes on sooner and pulls longer. This makes exiting a turn much easier, it pulls out of the turn before is hits peak power, then revs until the next turn. Much more ridable!!

Best of all, these mods are cheap, the only thing I spent that costs more than a routine top end job was the $130 for the V-Force.

Oh, and the motor doesn't rattle any more. Sounds good and tight. This is the way the CR should have came from the factory!!

Thanks Marcus and all the other DRN tuners for the info.
:) :) :) :) :)

 

[NO HAND]

Tell me if I'm wrong, but you sound as if you're only 50% impressed. I'm sure that the modification that is most responsible for the change in personnality of your engine is the thinner base gasket. This mod is aimed at shifting the powerband lower in the rpm by changing the port timing and increasing compression. This is probably why you might end up missing the raging top end you had before. It's easy to switch back anyway. I've tried all kinds gasket heights on my old 91cr125 to lower the deck height and increase compression and found that it is easy to remove the hit and lose the overrev that way. I personnaly didn't like that because that was not the type of powerband I was after. The two head gaskets recommended for 00 and up are another story. It is aimed to prevent damage from detonation. The other mods you made were known to only add without removing anywhere else.

 

[marcusgunby]

Jay good to hear you impressions- i would think the best mod next is a 38mm carb - more top end and overev from the 38mm carb.You can get one new from service honda for very resonable money.Also what jetting are you using as improvements can be made.

 

[NC514]

What year is your Honda Jay-R

I have an 02 Cr 125r just wonderiing so i could compare the results

 

[marcusgunby]

To add comments Nc on the 02
I modified mine last weekend
01 V force matched to 02 manifold.
Doma short silencer from the 01-only had to remove 15mm where the pipe enters the front pipe:)
Powervalve stop pin 7mm o/d
Husky piston
My impression were like Jays-overall a good increase in width of the powerband- a bit more top on the 02 as the exhaust port height is higher.
Pulled harder from the bottom up-i havent tried the cometic thin gasket yet as im not sure it needs it.
I did run 2 head gasket to stop detonation but have now had the head modded to this spec i made up on the way to the machinist.
1.1mm squish gap
6.5mm wide squish band
3 degree angle on squish band.
with about 0.5cc removed from the dome part
Plug recessed into head more (1mm) to allow it to sit properly in the combustion chamber(honda have made it wrong since i think 1990)

It goes on the dyno on friday hopefully ,and im looking to try a 38/39mm carbs and removing the reed spacer.

 

[Jay-R]

Marcus, I am axious to see how your mods turn out on the dyno. I will keep the bigger carb in mind. Right now, I am running the stock needle, slow jet and main. I have the clip set on the second groove and the air screw 3 turns out, I think. I have not had a chance to go to the track to try and fine tune it yet. I have read some reccommendations of running a smaller main and slow jet in the CR's. What is your opinion? Also, I am not sure what two stroke detonation sounds like. So I don't know what I need to listen for.

No Hand, I did not mean to give the wrong impression, I am very happy with my results for the money spent. However, I tend to understate power increases. I may have gained 1 to 2 horses. You are probably right that I gave up top end by using a thinner base gasket. Although really I probably just gave up the top end that I could have gained. I don't really believe that I have lost any, but I could be wrong. My goal was really to increase the spread of power, and I feel that I have accomplished that. I thought that I would try this setup and may decide to use two head gaskets. I just feel like I would have more power with more compression. But, since you have tryed many gasket setups, what is your opinion on using two head gaskets with the thinner base gasket?

Also, I tend to try to rely on bottom end power too much, since I am not really fast and I am more accustomed to riding four strokes.

Thanks for the advice.

NC, I have a '01 CR 125

 

[marcusgunby]

Jay the dyno is off for this weekend as Karl Prestwood is coming over to the states till tuesday so it will be after then:(

I think you need to try a 42 pilot with the As at 1.5turns at a starting point.
You can get a crisper throttle responce by modifying the slide to a 6.5 by filing the cresent part 1mm deeper and then sanding all edges smooth.

some detonation sounds like rocks in your engine but when mine went i couldnt hear a thing-the only true test is to pull the head and look for pin like marks on the piston crown especially at the edges.

 

[Jay-R]

Marcus, where can I get a #42 pilot? The stock one is a #40 and everything that I have seen goes in increments of 5. So the next size is a #45. Is there a #42 from another year model or brand that fits? Also, tell me more about filing the slide. Do you file 1mm around the arc? Isn't this part chromed, does it chip the chrome. I haven't taken my slide out since reading your post so I may be thinking of it wrong.

 

[marcusgunby]

Now im confused Jay-i thought the 01 came with a 45 pilot.If you are on a 40 you need a 38(or is it a 37.5)these mikunis are different to what im used to.All jets should be available from any good shop.It isnt anything special.
The slide you mark 1mm up from the std arc and file up to that mark in a nice side to side motion to make it an even arc.Just use some 1000grit wet and dry with some wd40 to polish the shape and edges.No chipping should occur.

 

[Jay-R]

Sorry about that, I just went and looked in the book and saw that it came with a 45. I came back to edit my post, but I was too late. I knew that you would be prompt with your response. ;)

All I have been able to find so far is a 40. But I will keep looking. At troy-racing.com, the microfishe shows 40, 45, 50 etc. Thanks for the info on filing the slide. Some days I just stay dazed and confused.:confused: