got a little update here and some Go Pro footage.

remember the right foot peg mount stud that was ground down on the end? I took a 12mm die and dressed up the threads and put the nut on.

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this is a video I made while the engine was warming up.


and a very quick ride. this bike is very quick! I think it will eat a stock DT400 for breakfast at this point. it will get even faster when the engine is broken in and tuned! it gets to 50 or 55 MPH in a very short distance. speedo was not hooked up in this run but the tach is hooked up.

this was moderate throttle ,no more than about half throttle. keep in mind the throttle does not open the slide all the way! I might have a fix for it and still be able to use the stock throttle cable as I have a slide that might fit but does not require as much cable travel.


the power delivery was smooth and very easy to use and it has huge gobs of torque. I did not catch this with the Go Pro yesterday but it easily lofts the front tire in second or third gear. it also gets much stronger as it gains revs but the power delivery is not at all explosive. it is almost like a RT1 on steroids.

it developed that characteristic DT400 type rattle. it can't be due to the piston clearance or wrist pin bearing or anything else engine related and it runs way too good to have problems. I have heard other DT400s make this sound and I don't know why...

it will rev like a 175 too!

I am wondering if the oil pump is the source of the typical enduro ticking sound. Did I just see the bike easily rev to over 8 or 9 grand. Not typical of a stock 400 that is for sure. That is some serious horsepower. I like it.

thanks Frank! the first time I ran it and it did not have the ticking noise but as it got a little run time,the ticking appeared.

my other DT400 does this too and did it since day 1 when I got it, as time and miles went by that ticking became accompanied with piston slap.

this engine has new main bearings and they have no play at all plus a crankshaft in decent shape and the wrist pin and bearing are a super nice fit. it rotates very smoothly but there is no radial or axial play at all. I am wondering if the oil pump by the way it is driven directly off the crankshaft is the culprit or maybe something else.

it only makes this sound at idle.

I had seen quite a few 1975-76 DT400s and even some DT250s make this noise.

the early engines had a jackshaft oil pump drive and they are some of the most mechanically quiet engines around, that is if you take the ringing fins in to account.

the MX400B made peak power at just a breath over 8000 rpm from the tests I read about it. the engine was hitting at least that when I goosed it. it behaves more like my 1978 DT175 does with no load. it flops the tach needle around like the 175 does when revved. this tach is the tach off the other DT400 and it was no where as hyper with it as this DT400 is.

well,tried experimenting with parts from a large body Mikuni VM36 carb today.

as I found out,the slide will not work, just a smidge too small. at least the length of the slide was about the same but not as big around. the place where the cable goes is at the bottom of the slide where the VM38 slide has a bracket and positions the end of the cable in a higher place.

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here is with the slide that goes with the VM38.

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this is the fit with the VM36 slide in the VM38 carb.

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lets see if this choke lever style will replace the annoying lift up and twist choke.

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hmm,maybe!

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both choke plungers the same length and diameter.

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so far so good!

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sweet! you can even hear the choke plunger click against the carb body when the choke is released!

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Ticking sounds like it may be the tach

it might be,I got another DT400 tach that I will put on a new face plate decal and install on the bike. if I remember correctly though it ticked without the tach hooked up too.

it started ticking after some running and heat cycles. very strange! it also has more compression than it did at the first start so the rings are bedding in. it is harder for me to kick past the compression stroke and the engine rolls through very smooth until it gets up on compression.

I don't think it is damage related or so I think. my first DT400 did it and numerous Youtube videos of DT400s tick too.

it just started making the ticking noise. when it is held at around 2000 rpm or over that, the ticking goes away.

I have heard a similar sound that was no more than gear rollover noise. this is on a truck and you can hear it with the engine idling and the trans in neutral with the clutch released. noise goes away when clutch is in and in gear. in this case the noise was normal.

I think I will ask Enduronut about it!

That noise in the truck is usually the Throw out bearing 9/10.The noise I hear in the video does not sound like it is from the mill but something bolted on,like the tach cable as it seems to keep tune with rpm.I suppose it is the same with the injector pump as well though,but my ear says not the motor itself.May check the heatshield on the pipe as well.In fact get off while it idles and lay your hands all over the machine and see if the tick changes.
When I was a kid,I had an old impala that developed a tick and dropped by my local garage to ask an old mech about it.He grabbed a long wooden stick and placed it here and there alongside his jaw near his ear and traced the noise down.

these were new trucks and people had brought them in for warranty service. one of the techs replaced the throw out bearing and that noise was still there.

all these trucks had the ZF transmissions in them and according to the Ford TSB it was a normal sound. these same trucks went on to run 50,000 miles to over 100.000 miles and had no trouble.

I read the TSB and yes I had people bring them in. 99% of the trucks had nothing wrong with them and a few had other causes for noise that was not normal and I repaired them under warranty.

the wildest one was a Taurus that came in and the customer brought it in for as the customer described as a "Mooing" noise. it was in the dead of winter and it turned out to be the ABS working normally like it should. when the ABS kicked in it made a sound under the hood where the ABS pump was and it also kicked the brake pedal a little as feedback and the car stopped straight and under control every time. there was once again a normal cause for this and it was working well all along. the customer after the explanation of it accepted it and continued bringing it to us for service and warranty work there at the Dealership and was a great customer.

I got word back from Enduronut through Instant message and he explained it and confirmed it was nothing to worry about.

we went with a Yamaha 510 Piston and it is a MX type piston and on the intake side there is not that much of a piston skirt there plus the bore was not enough to remove all the taper out of the cylinder near the exhaust port where the piston rocks very very little.

the MX engines because of the piston design tend to make a ticking sound when they run and have a few miles on them. he said basically there is nothing to worry about.

to make it more affordable he used a Yamaha piston 1 oversize up instead of a Wiseco which for what is available would have taken 2 oversizes up. I did not want to get it bored any more than necessary to get it to work anyway.

he also said the bore was clean in the power stroke area after the bore and I can confirm this to be true. the bike has tons of compression. sometime I will get out my compression gauge and test it. it has to have anywhere from 150 psi to 160 or 170 psi. my RT1M has 155 psi compression when I tested it and I suspect this one may have more. it is noticeably harder to kick in the compression stroke than the RT1M is.

I am pretty sure the compression release is working but it will not hurt to check it again.

took a VLC snapshot of the last video I made. in the part where the throttle is blipped,it hits a whopping 9500 rpm. pretty wild for a DT400!

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