facebook1 youtube1 twitter1 instagram linkedin1 pinterest1

NOTICE:  If you are not a free registered member of the site, you will not see the photos in the forum, and you won't be able to access our premium member content. Please consider joining our community! REGISTER AND MAKE THIS BOX DISAPPEAR!

×

Picture Attachment problem (09 Jul 2022)

Due to the extraordinary growth of the membership and resources, we are once again bumping up against hosting limits. I am working on a fix. In the meantime, the forum should function, but you won’t be able to attach images. Working as fast s we can to fix. Thanks for your patience. - Makotosun

RT1B compression .

  • shyted
  • shyted's Avatar Topic Author
  • Offline
  • Site Supporter
  • Site Supporter
  • Posts: 1153
  • Likes received: 735

RT1B compression . was created by shyted

A few months ago i commented about the pinging on the overrun on my RT1B.
I said about lowering the compression with the fitment of a thicker copper gasket .
I bought one from a manufacturer in Arizona after messaging to and fro for a few days.
The thickest one available to be cut from sheet without making it susceptible to splitting.
I fitted it as directed to the letter.
Also,i raised the needle by two notches on the carb.
The result, lots smoother running,you can start it without MX boots on and starts first kick every time hot or cold.
The thing is,there's no noticeable performance loss,in fact it's more responsive. The pinging seems to have subsided and the horrible overrun is loads less.
Still room for further improvement though. I have some ideas to try over winter.
Just so you know it works.
The following user(s) Liked this Post: Ht1kid, Pete-RT1, Sneezles61
Last edit: 22 Nov 2022 05:07 by shyted.
22 Nov 2022 05:04 #1

Please Log in or Create an account to join the conversation.

  • Posts: 919
  • Likes received: 332

Replied by AirborneSilva on topic RT1B compression .

A question and a thought: First, what do you mean by overrun? My thought is why couldn't you have just added a second gasket at the base of the cylinder instead of looking for a thicker head gasket? Just a thought...
1976 DT400C
1981 DT175H
1972 DT2 250
22 Nov 2022 05:24 #2

Please Log in or Create an account to join the conversation.

  • Posts: 1391
  • Likes received: 1082

Replied by 1971DT250 on topic RT1B compression .

What main jet do you have?
The hours spent riding my Enduros is not deducted from my life span.
22 Nov 2022 05:30 #3

Please Log in or Create an account to join the conversation.

  • Posts: 556
  • Likes received: 273

Replied by Sneezles61 on topic RT1B compression .

Now there’s something that’s got my interest… any pictures for comparison?
Sneezles61
22 Nov 2022 05:50 #4

Please Log in or Create an account to join the conversation.

  • Posts: 1060
  • Likes received: 494

Replied by msavitt on topic RT1B compression .

if overrun means engine going batshit crazy then you probably have an airleak. I had one once and it melted a hole in my piston and blew piston rings out my tail pipe!
The following user(s) Liked this Post: YamahaForumUsername
22 Nov 2022 08:38 #5

Please Log in or Create an account to join the conversation.

  • Posts: 30
  • Likes received: 7

Replied by automan on topic RT1B compression .

High R's and backing off the throttle.
Makes it lean and knocks is common.

cliff
22 Nov 2022 08:43 #6

Please Log in or Create an account to join the conversation.

  • Posts: 12773
  • Likes received: 7888

Replied by MarkT on topic RT1B compression .

"Pinging" and/or surging on decel is a complex issue...  closing throttle causes a rich condition and poor scavenging of exhaust gasses.  Engine will misfire and often in my experience the "pinging" is what is colloquially termed "pipe bang"...  unburned fuel is ignited and explodes in the pipe. 

(Years ago I came across a video with a camera pointed at the exhaust flange and with every "bang" on decelleration you could see a puff of smoke and the pipe bounce away from the engine slightly.) 

Engines with a better seal at the head pipe...  like some of the later Yamaha's with a solid flange holding pipe to head...  seem less likely to do this...  so fresh air getting drawn into exhaust from leaky connection at the head pipe could contribute to "pipe bang" in my experience.

There are also some theories that the ultra rich mixtures from misfires and the poor scavenging can result in very high compression pressures (fuel doesn't compress so a few cc's of extra fuel will raise compression pressure). With non-uniform conditions in the chamber a "pocket" of not-too-rich mixture preignites...  this type of "pinging" is usually accompanied by a brief surge of acceleration along with the "ping" in my experience. 

The engines larger than 250 seem more far more likely to have the "surge-ping" which is probably preignition.  I'm not sure anyone knows for sure.
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
The following user(s) Liked this Post: JayB, Ht1kid, Sneezles61
Last edit: 22 Nov 2022 11:35 by MarkT.
22 Nov 2022 11:33 #7

Please Log in or Create an account to join the conversation.

  • Posts: 556
  • Likes received: 273

Replied by Sneezles61 on topic RT1B compression .

Thank you for taking the time to pass along what your finding….
I’ve just got used to pulling in the clutch… but that’s road riding…
Sneezles61
22 Nov 2022 15:08 #8

Please Log in or Create an account to join the conversation.

  • Posts: 597
  • Likes received: 322

Replied by Ht1kid on topic RT1B compression .

Great write up MarkT!!!
22 Nov 2022 15:47 #9

Please Log in or Create an account to join the conversation.

  • Posts: 8721
  • Likes received: 3328

Replied by RT325 on topic RT1B compression .

Rig up some kind of cutout to stop the spark on de-celeration. Nothing to bang then. Naa, maybe not. How bout a compression ignition system like Honda had for a short while. How the hell did that work.
22 Nov 2022 16:23 #10

Please Log in or Create an account to join the conversation.

Moderators: yamadminEnduronutMakotosunDEETVinnieDevinJames Hart