Early 400 engines

I would be interested in knowing what, if any performance changes were made to the 400 engines (especially CR series) between 1970 and 1974. Were there port changes? Did the engine ever get reeds? My 70 model runs good, but could use more power getting to the first turn. Don't want to modify this 4 speed bike, but am watching the ads for a 5 speed 400. Having never ridden the 1972 to 1974 400, was wondering what to expect from the engine (assuming an unmodified engine).
Any comments appreciated.

The 400 topend is pretty much unchanged to the end.It was never reeded.As for getting to the first turn,to me the biggest issue is keeping the front wheel on the ground.I did add a reed to mine,but it's a special that some mods were done to make it work.

Reed valves were initially not used on engines over 250 because the Open bike usually had a broad powerband , if nothing else, because of the displacement volume. Reed valves starting with Yamaha and power jets were used by Honda with the power jets in the 1976 MR250 ( from the Gold Wing). Most 250s from that time frame were somewhat soft in the low/mid range before reed valves came in.

Thanks auto. Mine is stock, original expansion chamber, 36mm Bing, properly jetted. Timing set to 3.5mm per the service manual. Pulls cleanly and has a wide powerband. I believe it is performing as it should, but the Maico 400s beat me to the 1st turn. Of course, then I have to pass them . In all fairness, most of the bikes I race against are modified. I am going to be looking at a 1974 400 in a couple of weeks (its 300 miles away, hopefully it won't be sold before I can get there). This bike is original to my family, bought new by my dad. I've damaged the old 4 speed trans three times and gears are getting hard to find, so modifying for better performance is not in my plans.
But if I buy another one, I would consider doing so.
What do you run your timing at? What kind of response did you get by adding the reeds? Noticed your expansion chamber has been modified.
Appreciate your comments.
Steve

The pipe is a magnum,same as a retro rocket.I like more for the tighter fit and more leg room.The reed really helps.It's bigger than the gems and d&h reed blocks that are out there.Like I said,you need wheel base to keep the front end down.I just added a 78 arm.Trying some starts today.I hope it more dump the clutch and go.When a race is 4 to 5 laps,starts are everything.

On the piston ported engines we would cut 1/8" off the bottom of the piston to change the port timing. Then polish the exhaust port.

Thanks auto,
Same here, our races are typically 5 laps. Sounds like you are definitely producing more power than I am. Might ask some more questions if I get the 74. The 5 speed itself will probably be of help. One of the issues that comes into play is rider weight. As a 150 lb. teenager, my brother could leave the line in 2nd gear on this bike. With full gear, I am at 195 lbs., makes a big difference in the machines performance. Look forward to hearing how the swingarm works out.

Have you played with the front sprocket for your brother? One tooth larger to bring ratio down and speed the bike up he could leave harder.

Yes, in the past, have cut the piston skirt on some Pursangs (like they didn't scream already) as well as modified crankcase rotary valves on Kawasaki 350s. Have added piston ports, reeds and 36mm pumper carb to a 125 Aermacchi (Harley Rapido). All a long time ago, but the concept is clear. Haven't modified any of my Husqvarna, so any advice is helpful. Seems like info for the early machines is becoming harder to come by.

We took a 71 Suzuki ts125 and cut the piston 1/8". Added a set of kx80 shocks on the rear. Painted it metallic blue. Down the straights the kid was beating newer kx80's with the antique iron. The other kids were complaining. I heard the dad say that's a motorcycle. I did lower the front sprocket one tooth. It was so funny to watch. It's a antique dual sport. Now I wish I ported the cylinder.

This ts-125 had a broken main shaft in the tranny. We had a extra ts-185 engine. The main shaft was a 1/2" longer on the needle bearing end were the shaft on the 125 broke. Two minutes in a lathe fixed that. The same time I cut the piston.

These were our first bikes. We had ts-185, ts-100,ts-250, ts-400. Soon after the first 83 250 husqvarna milk truck eveloution bike was next.

Sorry for the confusion, when brother was racing as a teen it was 1970-72. Just meant to say that these machines are expected to perform well even though we are typically heavier riders with more safety gear on than when the bikes were new. With the 13 tooth C/S sprocket, overall ratio in 1st gear is approximately 18.5: 1. I can bring the revs up and simply dump the clutch. I have considered going to a 14 tooth C/S but it will probably require slipping the clutch while getting off the line. May get me rolling quicker, but the 4 speed clutches are not very large and not sure how it would take the abuse. I think the oval case 4 speeds started off designed in the late 50's for 250s, then had to handle 360cc, then by 1969 went to 400cc, more torque against same size gears and clutch. The clutch and trans just aren't very substantial for a 400cc machine in my opinion, though I absolutely love the bike. Heck, it's a family heirloom .
So, my choice to try to grab a 5 speed 400, while of course retaining my most prized motorcycle.

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I have no experience with this modification but I think it would help. Increasing flow and reducing turbulence always results in HP gain. How much and where on the RPM curve is another thing.

The exhaust port on these older Huskys have a huge cliff that surely creates a lot of turbulence. The 125 Husky factory modification includes a tongue welded to the exhaust manifold to ease the decline from a cliff to a ramp. How much of an improvement this would make in the 400's performance is anyones guess. Hope this helps out!

thats pretty sweet, just about all swedes could use that trick, lol

Yes, I have noticed that abrupt drop in the exhaust port on my cylinder. Seems like it would hinder flow. Would probably be worth trying that mod with another manifold. Then it would be easily reversible if necessary. I have also read that shortening the head pipe by 25mm at each end increases power and raises RPMs. Makes sense. Hadn't seen the port modifications shown in the article before. Just what I am looking for, a known performance modification with specs. Thanks much.
Now I'm going to have to have a 72-74 400 to investigate the suggestions. But then, three Huskies is nowhere near excessive from what I've seen on this forum.
Steve

I did that exhaust mod too.It's all the little things that add up. The 78 arm helped a lot,but it still wants to get the front end up.In two weeks I'll be at dilla,guess I will see then.