1981 Seca 750

I am a new rider. I bought an 81 XJ Seca 750 to learn on. Actually I had never even heard of this bike until a neighbour was selling his. Bike was in really good shape overall. Anyway....someone at work saw the bike and said that I should "bob" it. Never heard that term either. Googled "Yamaha XJ bobber" and loved what I saw. I have mechanical skills and also build guitars...so ya...this to me is very doable.

I have scoured the web for info, and like everything else there are so many variables in what can be done to this bike. So here are a few questions....
FRAME
The triple backbone poses a problem for tank fitment. I personally do not like the Maxim tank as I find once the back end of the frame is chopped just past the seat area...the front of the bike looks "bloated" to me. Again thats my opinion and not to offend anyone. Somewhere I saw someone remove the two smaller backbones and added on to the existing middle backbone closer to the neck of the frame. This would solve a lot of problems for tank fitment. Would this compromise the integrity of the frame..especially "twisting".
I am a sucker for the sportster type tanks. Cant help it. Loved that look since I was a kid.

REAR WHEEL TO FRONT WHEEL CONVERSION.
This would eliminate the double disks. If this is another issue what would be the widest tyre I could use on the wheel?

Gauges
Should I just re wire the entire thing or is there a set of gauges that would work with minimal change in wiring?

AIR INTAKE
I love the look of pods and have read up on the various issues associated with them. Is there an alternative such as some type of 4 into 1 filter fitting? Or maybe adding some type of a plug to each pod with a smaller opening to block the extra airflow which would eliminate rejetting and other issues.

This is where I am at this point with the machine. Any input would be appreciated. Thanks for reading folks.

 

Personally, for the amount of frame work necessary to fit a Sportster tank on that bike, I would modify the tunnel on the tank instead.

 

Ya I agree with bigshankhank

 

I would just buy a used sportster.

 

Well, that would always be my first choice, but didn't see that option in the poll.

 

while your at it, tip the frame up and stand it on it's tail. if it lived out in the weather for any length of time there might be water in it. now is the time to get it out.

 

Well it be cool if you get that tank in their without doing modification to the frame

 

I am leaning towards modifying the tank. Poluck.....good advice I will do that.

 

Show some pic cuz I will like to do that my my xj bike

 

under the swingarm pivot cover there should be a drain hole, make sure it's open. then you should see the open end of the lower frame rail in there, squirt some oil in there.

 

The peanut tanks holds little gas to start with ,modding the tunnel will result in less gas not to mention the risk of creating a leaky tank. I'm in favor of modding the frame, but you'll want to add a second lower bar to reinforce the backbone on use some gussets.
Pods are a hassle, the biggest problem with pods are the style carbs your putting them on. Get 4 Mikuni round slide carbs and the throttle/cable system that goes with them and you'll be better off. They cost around 80 bucks a piece, they are easier to adjust/clean and they handle air/exhaust mods a lot better. It will cost a little more in the beginning, but will save you more money, time and aggravation later. Just remember to get 2 lefts and 2 rights because they have choke levers on the carb bodies. You'll also need a larger petcock(5/16ths or 3/8ths), external fuel filter and fuel line.

 

Thanks OnB. When you say a second lower bar...do you mean directly under the main backbone or welded to the backbone.?

 

I was talking about a little lower than the other or use some gussets at each end to reinforce.

 

Got it. I will post pics for sure, but not a blow by blow of my every move. Once there is significant progress I will post. Thanks folks. If anyone has anything to add please do.

 

I ended up doing the backbone mod. Also removed the factory neck gusset. Due to the triple backbone being connected to the neck, the factory gussets did not seem strong enough. So I will be doing gussets maybe this week. I had bookmarked a lot of articles from the site but since the website change all the links have been lost.

My main concern has aways been the gauges. Since removing the big plastic thing....I am not sure what cluster will work with this bike. Would the Maxim of the same year work?

 

*Taps microphone*....."is this thing on?"


-Lets talk gauge cluster..lol

 

Lots of options on gauges, either digital or analog. What are you looking for?

 

There are some wiring modifications that need to be done to fit the Maxim guge cluster.

http://www.xjbikes.com/forums/index...ead-of-secas-i-have-the-answer-for-you.16481/


There are also some modifications that need to be done to fit a set of aftermarket gauges. The easiest way is to build a mounting box for the systems monitor, relocate it somewhere (one guy put it under the seat, another built a fancy bracket to house it on the bars between his new gauges), and then you can use the gauges of your choice.

The harder way involves bypasssing the systems monitor, while keeping the safety circuits intact.

 

Something like this.

 

I warn people away from those things, they don't hold up well against vibration. And motorcycles vibrate.

 

What would you recommend ?

 

http://www.mikesxs.net/products-46.html#products

 

great site. thanks k-moe.

 

What KMoe said...

 

This is where my Seca is at this point. Didn't get as much done as I thought I would because Ive just been too busy at work. This is after the backbone conversion. The solo seat is resting on the frame so I can get an idea of how I want to weld the tubing to mount the seat. i had to wait on that part of the frame until I got the seat...so the curve of the frame matches the seat. I have the bike jacked so the back shock mounts are exactly the length of the shocks that are on order. Presently working on new gussets for the neck and a few other places.

 

Would Part numbers 03-0744 and 03-0745 work on an 81 xj650 maxim?

 

You need a ratio of 60MPH=2,240 RPM.

 

Honestly I have no clue what that means, not a master mechanic I learn as I go and reading

 

It just means that it will work with the speedo drive that Yamaha put on the front wheel. The speedometer will display 60MPH when the speedo cable is turning 2,240 RPM. Any other speedometer ratio will be incorrect. The speedo you asked about has a ratio of 2:1.

 

Found a speedo with the correct ratio http://www.ebay.com/itm/Mini-Speedo...60-gauges-with-indicator-lights-/230981351004

 

a few of these will work as well http://www.partsnmore.com/parts/yamaha/xj550/?filters[category]=controls&filters[price]=100

 

good find

 

Just ordered this speedo. Man I have to tell this company is awesome any questions they will answer and help you how ever they can to see what is going to work correctly, the shipping is pretty fast. Company is based in Florida so since I am also in Florida their shipping is next day for me. I do Highly Recommend them.

http://www.dimecitycycles.com/2-5-i...with-white-face-and-led-indicator-lights.html

 

I am interested in a similar gauge cluster Voxboy. Any luck with yours?

 

I should be getting it any day. Not going to be put on bike for a while yet. Kris Taylor thanks for the links as well. I ordered the drag specialties

 

Your welcome

 

Got the frame back from welding and it looks great. I removed the original gussets and had new one's added as well. While I was at the welders garage I noticed some fuel tanks in his garage. I bought the tank that is in the pic below.....I love the look of this better than the King XL tank. What do you folks think? King tank or Mustang.

 

Honestly.....it needs a coffin tank. Of the two you have I prefer the Mustang.

 

A coffin tank would look cool on there.