Author Topic: Low speed running issue  (Read 275 times)

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Offline OSSAMAN

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Low speed running issue
« on: May 28, 2018, 11:49:35 AM »
Just picked up my first 400D. Been trailing for 45 years, 2t and 4t.

Don't know any history of the bike.

Plonking around from 0-10, using the first third of the throttle,  the bike cuts up badly, almost identical to stuck choke. But getting into the second third of throttle and up, no problem. Pulls like a freight train, clean and smooth, right into the upper revs.
But trying to navigate the slow technical stuff with a bike that is running terrible is maddening. I mean, it runs (meaning it doesn't die), and it will even idle sort of ok, but trying to slow power through rough terrain it coughs, pops, and doesn't produce any usable power.

The previous owner did tell me he replaced the intake manifold.

Other advice I would welcome;  I read a lot about bad crank seals. Is there a symptom that says they are bad? And base and head gaskets; what symptoms would indicate a small crack or leak? Are there common modifications to these gaskets that are advisable?

Thanks for any advice.

Offline Martin I Henry

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Re: Low speed running issue
« Reply #1 on: May 28, 2018, 05:14:04 PM »
Welcome to the forum OSSAMAN.

Traditionally, we have found this is a good place to say hello and introduce yourself: http://www.yamahait.com.au/forum/index.php/topic,1.1320.html

I have edited your post so it is a little more easy to read. That was a big lump of text to wade through !

My first suggestion is that you locate a service manual for your IT400D. There is one on this page : http://davesbikes.weebly.com/manuals.html

However, it is always better to have a paper copy when out in the workshop.

Your problems seem to be right where the IT400D should excel. My suggestion would be to go back to basics.
New plug and cap, clean carb, stock jetting, stock fuel/oil mixture, clean air filter, new crank seals, no air leaks etc.

I think you get the idea.

Cheers,

Dave R.

Offline OSSAMAN

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Re: Low speed running issue
« Reply #2 on: May 28, 2018, 11:22:07 PM »
Thanks Dave.

I appreciate your help. I'll format things better in the future. I can handle the basics, but I do have one technical question.

Regarding the crank seals I keep reading about. Does the failure simple allow oil past the seals or does the failure create a pressure problem between the top end and the bottom end? I'm fine with the disassembly side of things, but I may not know the physics.

Ossaman

Offline Martin I Henry

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Re: Low speed running issue
« Reply #3 on: May 28, 2018, 11:54:04 PM »

Quote
Regarding the crank seals I keep reading about. Does the failure simple allow oil past the seals or does the failure create a pressure problem between the top end and the bottom end?

Sometimes the seal can be blown from it's housing. In that case the answer could be both !

Most of the time a failed primary gear side seal leads to oil being drawn into the crankcase.

You really need to change those seals. It's not really something that needs to be talked about, you just need to do it !

Consumable parts for the old IT's are cheap and plentiful..... Go wild !

Cheers,

Dave R.

Offline fred99999au

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Re: Low speed running issue
« Reply #4 on: May 29, 2018, 08:03:33 AM »
And the dry side seal failing will allow air in and bottom end pressure out, making it run poorly. If it pulls too much air in it will lean out the mixture and then melt stuff you dont want melted.