03CRF450 Hotcam+HeadMod by Eric & Rich - Jetting question...

Yoken

~SPONSOR~
Oct 18, 2001
56
0
Hi Eric, Rich,

I finally got all the parts, rebuilt the engine and went for a test-ride last Sunday...Mmmm... not bad at all! The engine is a lot smoother down low and pulls strong in the mid range. It feels like going 1 or 2 teeth up on the rear sproket, while still pulling the stock 13/50. I really like the mod that you guys recommended. Thanks!

For those how how don't know, here is what has been done to the topend:
- Head porting
- new Hotcam
- Kibblewhite valve kit
- new piston Wiseco 13:1

I've a couple of questions though, that I'll share in this forum:

1- The bike seems to vibrate a bit more than before, especially at idle (I didn't feel it when riding). Am pretty sure I re-aligned the counter balancer properly, but I'll check again. Could it be from the new Wiseco 13:1 piston? Weight versus stock piston?

2- It is pretty hot and humid here in Nashville these days so I leaned out the jetting a bit:

- stock #42 pilot
- stock needle OBELR but with clip up 1 groove (in 4th)
- main jet dropped to #165
- pump squirt time reduced to minimum

I was at Crofton-KY for the test-ride, nice 80F with low humidity. Track was dry, hard-pack. Rode about an hour at low to mid range to break-in the new engine. Didn't rev the engine yet.

The spark plug insulator is dark brown, almost black, all around! Is that still too rich at the needle? (I'll check the WOT conditions later when I am in better shape...he he!)

What are your jetting guidelines with the above mods?

3- Compression test gives only 55 PSI using the kick-starter and with warm engine. Is it normal? The specs for the stock engine are 64 PSI @600 RPM...

Thanks again for your help,
Yoken.
 

Rich Rohrich

Moderator / BioHazard
LIFETIME SPONSOR
Jul 27, 1999
22,820
16,889
Chicago
Yoken said:
1- The bike seems to vibrate a bit more than before, especially at idle (I didn't feel it when riding). Am pretty sure I re-aligned the counter balancer properly, but I'll check again. Could it be from the new Wiseco 13:1 piston? Weight versus stock piston?
.

The Wiseco piston and pin combo is about .5 grams lighter than the OEM parts so weight differnces have no real effect.

Yoken said:
2- It is pretty hot and humid here in Nashville these days so I leaned out the jetting a bit:

- stock #42 pilot
- stock needle OBELR but with clip up 1 groove (in 4th)
- main jet dropped to #165
- pump squirt time reduced to minimum

I was at Crofton-KY for the test-ride, nice 80F with low humidity. Track was dry, hard-pack. Rode about an hour at low to mid range to break-in the new engine. Didn't rev the engine yet.

The spark plug insulator is dark brown, almost black, all around! Is that still too rich at the needle? (I'll check the WOT conditions later when I am in better shape...he he!)

What are your jetting guidelines with the above mods?
.

Depending on the fuel you run it's pretty common to have to lean out the pilot jet needle and main , but until you can do a proper WOT plug chop I would use the ride and feel method and not pay too much attention to the way the plug looks. When you are riding it easy it's tough to get enough heat in the plug to keep it clean regardless of the jetting so you'll see more carbon buildup than you would normally.

Yoken said:
3- Compression test gives only 55 PSI using the kick-starter and with warm engine. Is it normal? The specs for the stock engine are 64 PSI @600 RPM...

Yep, that's normal. There are a couple of things going on here that you have to take into account.
The Hot Cam closes the intake valve later than the OEM cam which will lower the final pressure you are reading. The Honda manual numbers are based on the earlier intake closing pressures.

As an example, if you close the intake valve 10 degrees later on the CRF it will lower the final cranking pressure by about 40 psi. Some of that is made up with the increase in compression ratio, where a one point increase in compression ratio will raise cranking pressure about 20 PSI (BTW all these numbers assume no compression relase active) you can see it will balance somewhat. I don't remember the exact degree differences between the Hot Cam and OEM off the top of my head, but hopefully this will make it clearer.

You'll also find that as it breaks in that the reading will be higher as well . Single ring piston designs need a good seal to keep from leaking becuase they don't have a second compression ring as a helper. As the ring seats leakage will be reduced and cranking pressure will tend to go up.

Last but not least your atmospheric conditions and gauge can influence the numbers some as well.

All in all I'd say you are good to go. :cool:

If you have any other questions I'll be happy to answer them.
 

Yoken

~SPONSOR~
Oct 18, 2001
56
0
Thanks for your quick reply, Rich.
I'll be back to you when I have some more hours on the bike.
Have a great day,
Yoken.
 

Yoken

~SPONSOR~
Oct 18, 2001
56
0
Deansfastway,

That's what I did: one hand on the throttle wide open and the other on the kill switch...
I'll ride a few hours than will test again, see if it makes a difference.

Have a great weekend,
Eric
 

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